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diff --git a/doc/dnssec-guide/advanced-discussions.rst b/doc/dnssec-guide/advanced-discussions.rst new file mode 100644 index 0000000..692b189 --- /dev/null +++ b/doc/dnssec-guide/advanced-discussions.rst @@ -0,0 +1,1089 @@ +.. Copyright (C) Internet Systems Consortium, Inc. ("ISC") +.. +.. SPDX-License-Identifier: MPL-2.0 +.. +.. This Source Code Form is subject to the terms of the Mozilla Public +.. License, v. 2.0. If a copy of the MPL was not distributed with this +.. file, you can obtain one at https://mozilla.org/MPL/2.0/. +.. +.. See the COPYRIGHT file distributed with this work for additional +.. information regarding copyright ownership. + +.. _dnssec_advanced_discussions: + +Advanced Discussions +-------------------- + +.. _signature_validity_periods: + +Signature Validity Periods and Zone Re-Signing Intervals +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +In :ref:`how_are_answers_verified`, we saw that record signatures +have a validity period outside of which they are not valid. This means +that at some point, a signature will no longer be valid and a query for +the associated record will fail DNSSEC validation. But how long should a +signature be valid for? + +The maximum value for the validity period should be determined by the impact of a +replay attack: if this is low, the period can be long; if high, +the period should be shorter. There is no "right" value, but periods of +between a few days to a month are common. + +Deciding a minimum value is probably an easier task. Should something +fail (e.g., a hidden primary distributing to secondary servers that +actually answer queries), how long will it take before the failure is +noticed, and how long before it is fixed? If you are a large 24x7 +operation with operators always on-site, the answer might be less than +an hour. In smaller companies, if the failure occurs +just after everyone has gone home for a long weekend, the answer might +be several days. + +Again, there are no "right" values - they depend on your circumstances. The +signature validity period you decide to use should be a value between +the two bounds. At the time of this writing (mid-2020), the default policy used by BIND +sets a value of 14 days. + +To keep the zone valid, the signatures must be periodically refreshed +since they expire - i.e., the zone must be periodically +re-signed. The frequency of the re-signing depends on your network's +individual needs. For example, signing puts a load on your server, so if +the server is very highly loaded, a lower re-signing frequency is better. Another +consideration is the signature lifetime: obviously the intervals between +signings must not be longer than the signature validity period. But if +you have set a signature lifetime close to the minimum (see above), the +signing interval must be much shorter. What would happen if the system +failed just before the zone was re-signed? + +Again, there is no single "right" answer; it depends on your circumstances. The +BIND 9 default policy sets the signature refresh interval to 5 days. + +.. _advanced_discussions_proof_of_nonexistence: + +Proof of Non-Existence (NSEC and NSEC3) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +How do you prove that something does not exist? This zen-like question +is an interesting one, and in this section we provide an overview +of how DNSSEC solves the problem. + +Why is it even important to have authenticated denial of existence in DNS? +Couldn't we just send back "hey, what you asked for does not exist," +and somehow generate a digital signature to go with it, proving it +really is from the correct authoritative source? Aside from the technical +challenge of signing something that doesn't exist, this solution has flaws, one of +which is it gives an attacker a way to create the appearance of denial +of service by replaying this message on the network. + +Let's use a little story, told three different ways, to +illustrate how proof of nonexistence works. In our story, we run a small +company with three employees: Alice, Edward, and Susan. For reasons that +are far too complicated to go into, they don't have email accounts; +instead, email for them is sent to a single account and a nameless +intern passes the message to them. The intern has access to our private +DNSSEC key to create signatures for their responses. + +If we followed the approach of giving back the same answer no matter +what was asked, when people emailed and asked for the message to be +passed to "Bob," our intern would simply answer "Sorry, that person +doesn’t work here" and sign this message. This answer could be validated +because our intern signed the response with our private DNSSEC key. +However, since the signature doesn’t change, an attacker could record +this message. If the attacker were able to intercept our email, when the next +person emailed asking for the message to be passed to Susan, the attacker +could return the exact same message: "Sorry, that person doesn’t work +here," with the same signature. Now the attacker has successfully fooled +the sender into thinking that Susan doesn’t work at our company, and +might even be able to convince all senders that no one works at this +company. + +To solve this problem, two different solutions were created. We will +look at the first one, NSEC, next. + +.. _advanced_discussions_nsec: +.. _NSEC: + +NSEC +^^^^ + +The NSEC record is used to prove that something does not exist, by +providing the name before it and the name after it. Using our tiny +company example, this would be analogous to someone sending an email for +Bob and our nameless intern responding with with: "I'm sorry, that +person doesn't work here. The name before the location where 'Bob' +would be is Alice, and the name after that is Edward." Let's say +another email was received for a +non-existent person, this time Oliver; our intern would respond "I'm +sorry, that person doesn't work here. The name before the location +where 'Oliver' would be is Edward, +and the name after that is Susan." If another sender asked for Todd, the +answer would be: "I'm sorry, that person doesn't work here. The name +before the location where 'Todd' would be is Susan, and there are no +other names after that." + +So we end up with four NSEC records: + +:: + + example.com. 300 IN NSEC alice.example.com. A RRSIG NSEC + alice.example.com. 300 IN NSEC edward.example.com. A RRSIG NSEC + edward.example.com. 300 IN NSEC susan.example.com. A RRSIG NSEC + susan.example.com. 300 IN NSEC example.com. A RRSIG NSEC + +What if the attacker tried to use the same replay method described +earlier? If someone sent an email for Edward, none of the four answers +would fit. If attacker replied with message #2, "I'm sorry, that person +doesn't work here. The name before it is Alice, and the name after it is +Edward," it is obviously false, since "Edward" is in the response; and the same +goes for #3, Edward and Susan. As for #1 and #4, Edward does not fall in +the alphabetical range before Alice or after Susan, so the sender can logically deduce +that it was an incorrect answer. + +When BIND signs your zone, the zone data is automatically sorted on +the fly before generating NSEC records, much like how a phone directory +is sorted. + +The NSEC record allows for a proof of non-existence for record types. If +you ask a signed zone for a name that exists but for a record type that +doesn't (for that name), the signed NSEC record returned lists all of +the record types that *do* exist for the requested domain name. + +NSEC records can also be used to show whether a record was generated as +the result of a wildcard expansion. The details of this are not +within the scope of this document, but are described well in +:rfc:`7129`. + +Unfortunately, the NSEC solution has a few drawbacks, one of which is +trivial "zone walking." In our story, a curious person can keep sending emails, and +our nameless, gullible intern keeps divulging information about our +employees. Imagine if the sender first asked: "Is Bob there?" and +received back the names Alice and Edward. Our sender could then email +again: "Is Edwarda there?", and will get back Edward and Susan. (No, +"Edwarda" is not a real name. However, it is the first name +alphabetically after "Edward" and that is enough to get the intern to reply +with a message telling us the next valid name after Edward.) Repeat the +process enough times and the person sending the emails eventually +learns every name in our company phone directory. For many of you, this +may not be a problem, since the very idea of DNS is similar to a public +phone book: if you don't want a name to be known publicly, don't put it +in DNS! Consider using DNS views (split DNS) and only display your +sensitive names to a select audience. + +The second potential drawback of NSEC is a bigger zone file and memory consumption; +there is no opt-out mechanism for insecure child zones, so each name +in the zone will get an additional NSEC record and a RRSIG record to go with +it. In practice this is a problem only for parent-zone operators dealing with +mostly insecure child zones, such as ``com.``. To learn more about opt-out, +please see :ref:`advanced_discussions_nsec3_optout`. + +.. _advanced_discussions_nsec3: +.. _nsec3: + +NSEC3 +^^^^^ + +NSEC3 adds two additional features that NSEC does not have: + +1. It offers no easy zone enumeration. + +2. It provides a mechanism for the parent zone to exclude insecure + delegations (i.e., delegations to zones that are not signed) from the + proof of non-existence. + +Recall that in :ref:`advanced_discussions_nsec` we provided a range of +names to prove that something does not exist. But as it turns +out, even disclosing these ranges of names becomes a problem: this made +it very easy for the curious-minded to look at our entire zone. Not +only that, unlike a zone transfer, this "zone walking" is more +resource-intensive. So how do we disclose something without actually disclosing +it? + +The answer is actually quite simple: hashing functions, or one-way +hashes. Without going into many details, think of it like a magical meat +grinder. A juicy piece of ribeye steak goes in one end, and out comes a +predictable shape and size of ground meat (hash) with a somewhat unique +pattern. No matter how hard you try, you cannot turn the ground meat +back into the ribeye steak: that's what we call a one-way hash. + +NSEC3 basically runs the names through a one-way hash before giving them +out, so the recipients can verify the non-existence without any +knowledge of the other names in the zone. + +So let's tell our little story for the third time, this +time with NSEC3. In this version, our intern is not given a list of actual +names; he is given a list of "hashed" names. So instead of Alice, +Edward, and Susan, the list he is given reads like this (hashes +shortened for easier reading): + +:: + + FSK5.... (produced from Edward) + JKMA.... (produced from Susan) + NTQ0.... (produced from Alice) + +Then, an email is received for Bob again. Our intern takes the name Bob +through a hash function, and the result is L8J2..., so he replies: "I'm +sorry, that person doesn't work here. The name before that is JKMA..., +and the name after that is NTQ0...". There, we proved Bob doesn't exist, +without giving away any names! To put that into proper NSEC3 resource +records, they would look like this (again, hashes shortened for +ease of display): + +:: + + FSK5....example.com. 300 IN NSEC3 1 0 0 - JKMA... A RRSIG + JKMA....example.com. 300 IN NSEC3 1 0 0 - NTQ0... A RRSIG + NTQ0....example.com. 300 IN NSEC3 1 0 0 - FSK5... A RRSIG + +.. note:: + + Just because we employed one-way hash functions does not mean there is + no way for a determined individual to figure out our zone data. + +Most names published in the DNS are rarely secret or unpredictable. They are +published to be memorable, used and consumed by humans. They are often recorded +in many other network logs such as email logs, certificate transparency logs, +web page links, intrusion detection systems, malware scanners, email archives, +etc. Many times a simple dictionary of commonly used domain-name prefixes +(www, mail, imap, login, database, etc.) can be used to quickly reveal a large +number of labels within a zone. Additionally, if an adversary really wants to +expend significant CPU resources to mount an offline dictionary attack on a +zone's NSEC3 chain, they will likely be able to find most of the "guessable" +names despite any level of hashing. + +Also, it is still possible to gather all of our NSEC3 records and hashed +names and perform an offline brute-force attack by trying all +possible combinations to figure out what the original name is. In our +meat-grinder analogy, this would be like someone +buying all available cuts of meat and grinding them up at home using +the same model of meat grinder, and comparing the output with the meat +you gave him. It is expensive and time-consuming (especially with +real meat), but like everything else in cryptography, if someone has +enough resources and time, nothing is truly private forever. If you +are concerned about someone performing this type of attack on your +zone data, use some of the special techniques described in :rfc:`4470`. + +.. _advanced_discussions_nsec3param: + +NSEC3PARAM +++++++++++ + +.. warning:: + Before we dive into the details of NSEC3 parametrization, please note: + the defaults should not be changed without a strong justification and a full + understanding of the potential impact. + +The above NSEC3 examples used four parameters: 1, 0, 0, and +zero-length salt. 1 represents the algorithm, 0 represents the opt-out +flag, 0 represents the number of additional iterations, and - is the +salt. Let's look at how each one can be configured: + +.. glossary:: + + Algorithm + NSEC3 Hashing Algorithm + The only currently defined value is 1 for SHA-1, so there + is no configuration field for it. + + Opt-out + Setting this bit to 1 enables NSEC3 opt-out, which is + discussed in :ref:`advanced_discussions_nsec3_optout`. + + Iterations + Iterations defines the number of _additional_ times to + apply the algorithm when generating an NSEC3 hash. More iterations + consume more resources for both authoritative servers and validating + resolvers. The considerations here are similar to those seen in + :ref:`key_sizes`, of security versus resources. + + .. warning:: + Do not use values higher than zero. A value of zero provides one round + of SHA-1 hashing and protects from non-determined attackers. + + A greater number of additional iterations causes interoperability problems + and opens servers to CPU-exhausting DoS attacks, while providing + only doubtful security benefits. + + Salt + A salt value, which can be combined with an FQDN to influence the + resulting hash. Salt is discussed in more detail in + :ref:`advanced_discussions_nsec3_salt`. + +.. _advanced_discussions_nsec3_optout: + +NSEC3 Opt-Out ++++++++++++++ + +First things first: For most DNS administrators who do not manage a huge number +of insecure delegations, the NSEC3 opt-out featuere is not relevant. + +Opt-out allows for blocks of unsigned delegations to be covered by a single NSEC3 +record. In other words, use of the opt-out allows large registries to only sign as +many NSEC3 records as there are signed DS or other RRsets in the zone; with +opt-out, unsigned delegations do not require additional NSEC3 records. This +sacrifices the tamper-resistance proof of non-existence offered by NSEC3 in +order to reduce memory and CPU overheads, and decreases the effectiveness of the cache +(:rfc:`8198`). + +Why would that ever be desirable? If a significant number of delegations +are not yet securely delegated, meaning they lack DS records and are still +insecure or unsigned, generating DNSSEC records for all their NS records +might consume lots of memory and is not strictly required by the child zones. + +This resource-saving typically makes a difference only for *huge* zones like ``com.``. +Imagine that you are the operator of busy top-level domains such as ``com.``, +with millions of insecure delegated domain names. +As of mid-2022, around 3% of all ``com.`` zones are signed. Basically, +without opt-out, with 1,000,000 delegations, only 30,000 of which are secure, you +still have to generate NSEC RRsets for the other 970,000 delegations; with +NSEC3 opt-out, you will have saved yourself 970,000 sets of records. + +In contrast, for a small zone the difference is operationally negligible +and the drawbacks outweigh the benefits. + +If NSEC3 opt-out is truly essential for a zone, the following +configuration can be added to ``dnssec-policy``; for example, to create an +NSEC3 chain using the SHA-1 hash algorithm, with the opt-out flag, +no additional iterations, and no extra salt, use: + +.. code-block:: none + + dnssec-policy "nsec3" { + ... + nsec3param iterations 0 optout yes salt-length 0; + }; + + + +To learn more about how to configure NSEC3 opt-out, please see +:ref:`recipes_nsec3_optout`. + +.. _advanced_discussions_nsec3_salt: + +NSEC3 Salt +++++++++++ + +.. warning:: + Contrary to popular belief, adding salt provides little value. + Each DNS zone is always uniquely salted using the zone name. **Operators should + use a zero-length salt value.** + +The properties of this extra salt are complicated and beyond scope of this +document. For detailed description why the salt in the context of DNSSEC +provides little value please see `IETF draft ietf-dnsop-nsec3-guidance version +10 section 2.4 +<https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-nsec3-guidance-10#section-2.4>`__. + +.. _advanced_discussions_nsec_or_nsec3: + +NSEC or NSEC3? +^^^^^^^^^^^^^^ + +So which is better: NSEC or NSEC3? There is no single right +answer here that fits everyone; it comes down to a given network's needs or +requirements. + +In most cases, NSEC is a good choice for zone administrators. It +relieves the authoritative servers and resolver of the additional cryptographic +operations that NSEC3 requires, and NSEC is comparatively easier to +troubleshoot than NSEC3. + +NSEC3 comes with many drawbacks and should be implemented only if zone +enumeration prevention is really needed, or when opt-out provides a +significant reduction in memory and CPU overheads (in other words, with a +huge zone with mostly insecure delegations). + +.. _advanced_discussions_key_generation: + +DNSSEC Keys +~~~~~~~~~~~ + +Types of Keys +^^^^^^^^^^^^^ + +Although DNSSEC +documentation talks about three types of keys, they are all the same +thing - but they have different roles. The roles are: + +Zone-Signing Key (ZSK) + This is the key used to sign the zone. It signs all records in the + zone apart from the DNSSEC key-related RRsets: DNSKEY, CDS, and + CDNSKEY. + +Key-Signing Key (KSK) + This is the key used to sign the DNSSEC key-related RRsets and is the + key used to link the parent and child zones. The parent zone stores a + digest of the KSK. When a resolver verifies the chain of trust it + checks to see that the DS record in the parent (which holds the + digest of a key) matches a key in the DNSKEY RRset, and that it is + able to use that key to verify the DNSKEY RRset. If it can do + that, the resolver knows that it can trust the DNSKEY resource + records, and so can use one of them to validate the other records in + the zone. + +Combined Signing Key (CSK) + A CSK combines the functionality of a ZSK and a KSK. Instead of + having one key for signing the zone and one for linking the parent + and child zones, a CSK is a single key that serves both roles. + +It is important to realize the terms ZSK, KSK, and CSK describe how the +keys are used - all these keys are represented by DNSKEY records. The +following examples are the DNSKEY records from a zone signed with a KSK +and ZSK: + +:: + + $ dig @192.168.1.12 example.com DNSKEY + + ; <<>> DiG 9.16.0 <<>> @192.168.1.12 example.com dnskey +multiline + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 54989 + ;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1 + ;; WARNING: recursion requested but not available + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags:; udp: 4096 + ; COOKIE: 5258d7ed09db0d76010000005ea1cc8c672d8db27a464e37 (good) + ;; QUESTION SECTION: + ;example.com. IN DNSKEY + + ;; ANSWER SECTION: + example.com. 60 IN DNSKEY 256 3 13 ( + tAeXLtIQ3aVDqqS/1UVRt9AE6/nzfoAuaT1Vy4dYl2CK + pLNcUJxME1Z//pnGXY+HqDU7Gr5HkJY8V0W3r5fzlw== + ) ; ZSK; alg = ECDSAP256SHA256 ; key id = 63722 + example.com. 60 IN DNSKEY 257 3 13 ( + cxkNegsgubBPXSra5ug2P8rWy63B8jTnS4n0IYSsD9eW + VhiyQDmdgevKUhfG3SE1wbLChjJc2FAbvSZ1qk03Nw== + ) ; KSK; alg = ECDSAP256SHA256 ; key id = 42933 + +... and a zone signed with just a CSK: + +:: + + $ dig @192.168.1.13 example.com DNSKEY + + ; <<>> DiG 9.16.0 <<>> @192.168.1.13 example.com dnskey +multiline + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 22628 + ;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1 + ;; WARNING: recursion requested but not available + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags:; udp: 4096 + ; COOKIE: bf19ee914b5df46e010000005ea1cd02b66c06885d274647 (good) + ;; QUESTION SECTION: + ;example.com. IN DNSKEY + + ;; ANSWER SECTION: + example.com. 60 IN DNSKEY 257 3 13 ( + p0XM6AJ68qid2vtOdyGaeH1jnrdk2GhZeVvGzXfP/PNa + 71wGtzR6jdUrTbXo5Z1W5QeeJF4dls4lh4z7DByF5Q== + ) ; KSK; alg = ECDSAP256SHA256 ; key id = 1231 + +The only visible difference between the records (apart from the key data +itself) is the value of the flags fields; this is 256 +for a ZSK and 257 for a KSK or CSK. Even then, the flags field is only a +hint to the software using it as to the role of the key: zones can be +signed by any key. The fact that a CSK and KSK both have the same flags +emphasizes this. A KSK usually only signs the DNSSEC key-related RRsets +in a zone, whereas a CSK is used to sign all records in the zone. + +The original idea of separating the function of the key into a KSK and +ZSK was operational. With a single key, changing it for any reason is +"expensive," as it requires interaction with the parent zone +(e.g., uploading the key to the parent may require manual interaction +with the organization running that zone). By splitting it, interaction +with the parent is required only if the KSK is changed; the ZSK can be +changed as often as required without involving the parent. + +The split also allows the keys to be of different lengths. So the ZSK, +which is used to sign the record in the zone, can be of a (relatively) +short length, lowering the load on the server. The KSK, which is used +only infrequently, can be of a much longer length. The relatively +infrequent use also allows the private part of the key to be stored in a +way that is more secure but that may require more overhead to access, e.g., on +an HSM (see :ref:`hardware_security_modules`). + +In the early days of DNSSEC, the idea of splitting the key went more or +less unchallenged. However, with the advent of more powerful computers +and the introduction of signaling methods between the parent and child +zones (see :ref:`cds_cdnskey`), the advantages of a ZSK/KSK split are +less clear and, for many zones, a single key is all that is required. + +As with many questions related to the choice of DNSSEC policy, the +decision on which is "best" is not clear and depends on your circumstances. + +Which Algorithm? +^^^^^^^^^^^^^^^^ + +There are three algorithm choices for DNSSEC as of this writing +(mid-2020): + +- RSA + +- Elliptic Curve DSA (ECDSA) + +- Edwards Curve Digital Security Algorithm (EdDSA) + +All are supported in BIND 9, but only RSA and ECDSA (specifically +RSASHA256 and ECDSAP256SHA256) are mandatory to implement in DNSSEC. +However, RSA is a little long in the tooth, and ECDSA/EdDSA are emerging +as the next new cryptographic standards. In fact, the US federal +government recommended discontinuing RSA use altogether by September 2015 +and migrating to using ECDSA or similar algorithms. + +For now, use ECDSAP256SHA256 but keep abreast of developments in this +area. For details about rolling over DNSKEYs to a new algorithm, see +:ref:`advanced_discussions_DNSKEY_algorithm_rollovers`. + +.. _key_sizes: + +Key Sizes +^^^^^^^^^ + +If using RSA keys, the choice of key sizes is a classic issue of finding +the balance between performance and security. The larger the key size, +the longer it takes for an attacker to crack the key; but larger keys +also mean more resources are needed both when generating signatures +(authoritative servers) and verifying signatures (recursive servers). + +Of the two sets of keys, ZSK is used much more frequently. ZSK is used whenever zone +data changes or when signatures expire, so performance +certainly is of a bigger concern. As for KSK, it is used less +frequently, so performance is less of a factor, but its impact is bigger +because of its role in signing other keys. + +In earlier versions of this guide, the following key lengths were +chosen for each set, with the recommendation that they be rotated more +frequently for better security: + +- *ZSK*: RSA 1024 bits, rollover every year + +- *KSK*: RSA 2048 bits, rollover every five years + +These should be considered minimum RSA key sizes. At the time +of this writing (mid-2020), the root zone and many TLDs are already using 2048 +bit ZSKs. If you choose to implement larger key sizes, keep in mind that +larger key sizes result in larger DNS responses, which this may mean more +load on network resources. Depending on your network configuration, end users +may even experience resolution failures due to the increased response +sizes, as discussed in :ref:`whats_edns0_all_about`. + +ECDSA key sizes can be much smaller for the same level of security, e.g., +an ECDSA key length of 224 bits provides the same level of security as a +2048-bit RSA key. Currently BIND 9 sets a key size of 256 for all ECDSA keys. + +.. _advanced_discussions_key_storage: + +Key Storage +^^^^^^^^^^^ + +Public Key Storage +++++++++++++++++++ + +The beauty of a public key cryptography system is that the public key +portion can and should be distributed to as many people as possible. As +the administrator, you may want to keep the public keys on an easily +accessible file system for operational ease, but there is no need to +securely store them, since both ZSK and KSK public keys are published in +the zone data as DNSKEY resource records. + +Additionally, a hash of the KSK public key is also uploaded to the +parent zone (see :ref:`working_with_parent_zone` for more details), +and is published by the parent zone as DS records. + +Private Key Storage ++++++++++++++++++++ + +Ideally, private keys should be stored offline, in secure devices such +as a smart card. Operationally, however, this creates certain +challenges, since the private key is needed to create RRSIG resource +records, and it is a hassle to bring the private key out of +storage every time the zone file changes or signatures expire. + +A common approach to strike the balance between security and +practicality is to have two sets of keys: a ZSK set and a KSK set. A ZSK +private key is used to sign zone data, and can be kept online for ease +of use, while a KSK private key is used to sign just the DNSKEY (the ZSK); it is +used less frequently, and can be stored in a much more secure and +restricted fashion. + +For example, a KSK private key stored on a USB flash drive that is kept +in a fireproof safe, only brought online once a year to sign a new pair +of ZSKs, combined with a ZSK private key stored on the network +file system and available for routine use, may be a good balance between +operational flexibility and security. + +For more information on changing keys, please see +:ref:`key_rollovers`. + +.. _hardware_security_modules: + +Hardware Security Modules (HSMs) +++++++++++++++++++++++++++++++++ + +A Hardware Security Module (HSM) may come in different shapes and sizes, +but as the name indicates, it is a physical device or devices, usually +with some or all of the following features: + +- Tamper-resistant key storage + +- Strong random-number generation + +- Hardware for faster cryptographic operations + +Most organizations do not incorporate HSMs into their security practices +due to cost and the added operational complexity. + +BIND supports Public Key Cryptography Standard #11 (PKCS #11) for +communication with HSMs and other cryptographic support devices. For +more information on how to configure BIND to work with an HSM, please +refer to the `BIND 9 Administrator Reference +Manual <https://bind9.readthedocs.io/en/latest/index.html>`_. + +.. _advanced_discussions_key_management: + +Rollovers +~~~~~~~~~ + +.. _key_rollovers: + +Key Rollovers +^^^^^^^^^^^^^ + +A key rollover is where one key in a zone is replaced by a new one. +There are arguments for and against regularly rolling keys. In essence +these are: + +Pros: + +1. Regularly changing the key hinders attempts at determination of the + private part of the key by cryptanalysis of signatures. + +2. It gives administrators practice at changing a key; should a key ever need to be + changed in an emergency, they would not be doing it for the first time. + +Cons: + +1. A lot of effort is required to hack a key, and there are probably + easier ways of obtaining it, e.g., by breaking into the systems on + which it is stored. + +2. Rolling the key adds complexity to the system and introduces the + possibility of error. We are more likely to + have an interruption to our service than if we had not rolled it. + +Whether and when to roll the key is up to you. How serious would the +damage be if a key were compromised without you knowing about it? How +serious would a key roll failure be? + +Before going any further, it is worth noting that if you sign your zone +with either of the fully automatic methods (described in ref:`signing_alternative_ways`), +you don't really need to +concern yourself with the details of a key rollover: BIND 9 takes care of +it all for you. If you are doing a manual key roll or are setting up the +keys for a semi-automatic key rollover, you do need to familiarize yourself +with the various steps involved and the timing details. + +Rolling a key is not as simple as replacing the DNSKEY statement in the +zone. That is an essential part of it, but timing is everything. For +example, suppose that we run the ``example.com`` zone and that a friend +queries for the AAAA record of ``www.example.com``. As part of the +resolution process (described in +:ref:`how_does_dnssec_change_dns_lookup`), their recursive server +looks up the keys for the ``example.com`` zone and uses them to verify +the signature associated with the AAAA record. We'll assume that the +records validated successfully, so they can use the +address to visit ``example.com``'s website. + +Let's also assume that immediately after the lookup, we want to roll the ZSK +for ``example.com``. Our first attempt at this is to remove the old +DNSKEY record and signatures, add a new DNSKEY record, and re-sign the +zone with it. So one minute our server is serving the old DNSKEY and +records signed with the old key, and the next minute it is serving the +new key and records signed with it. We've achieved our goal - we are +serving a zone signed with the new keys; to check this is really the +case, we booted up our laptop and looked up the AAAA record +``ftp.example.com``. The lookup succeeded so all must be well. Or is it? +Just to be sure, we called our friend and asked them to check. They +tried to lookup ``ftp.example.com`` but got a SERVFAIL response from +their recursive server. What's going on? + +The answer, in a word, is "caching." When our friend looked up +``www.example.com``, their recursive server retrieved and cached +not only the AAAA record, but also a lot of other records. It cached +the NS records for ``com`` and ``example.com``, as well as +the AAAA (and A) records for those name servers (and this action may, in turn, have +caused the lookup and caching of other NS and AAAA/A records). Most +importantly for this example, it also looked up and cached the DNSKEY +records for the root, ``com``, and ``example.com`` zones. When a query +was made for ``ftp.example.com``, the recursive server believed it +already had most of the information +we needed. It knew what nameservers served ``example.com`` and their +addresses, so it went directly to one of those to get the AAAA record for +``ftp.example.com`` and its associated signature. But when it tried to +validate the signature, it used the cached copy of the DNSKEY, and that +is when our friend had the problem. Their recursive server had a copy of +the old DNSKEY in its cache, but the AAAA record for ``ftp.example.com`` +was signed with the new key. So, not surprisingly, the signature could not +validate. + +How should we roll the keys for ``example.com``? A clue to the +answer is to note that the problem came about because the DNSKEY records +were cached by the recursive server. What would have happened had our +friend flushed the DNSKEY records from the recursive server's cache before +making the query? That would have worked; those records would have been +retrieved from ``example.com``'s nameservers at the same time that we +retrieved the AAAA record for ``ftp.example.com``. Our friend's server would have +obtained the new key along with the AAAA record and associated signature +created with the new key, and all would have been well. + +As it is obviously impossible for us to notify all recursive server +operators to flush our DNSKEY records every time we roll a key, we must +use another solution. That solution is to wait +for the recursive servers to remove old records from caches when they +reach their TTL. How exactly we do this depends on whether we are trying +to roll a ZSK, a KSK, or a CSK. + +.. _zsk_rollover_methods: + +ZSK Rollover Methods +++++++++++++++++++++ + +The ZSK can be rolled in one of the following two ways: + +1. *Pre-Publication*: Publish the new ZSK into zone data before it is + actually used. Wait at least one TTL interval, so the world's recursive servers + know about both keys, then stop using the old key and generate a new + RRSIG using the new key. Wait at least another TTL, so the cached old + key data is expunged from the world's recursive servers, and then remove + the old key. + + The benefit of the pre-publication approach is it does not + dramatically increase the zone size; however, the duration of the rollover + is longer. If insufficient time has passed after the new ZSK is + published, some resolvers may only have the old ZSK cached when the + new RRSIG records are published, and validation may fail. This is the + method described in :ref:`recipes_zsk_rollover`. + +2. *Double-Signature*: Publish the new ZSK and new RRSIG, essentially + doubling the size of the zone. Wait at least one TTL interval, and then remove + the old ZSK and old RRSIG. + + The benefit of the double-signature approach is that it is easier to + understand and execute, but it causes a significantly increased zone size + during a rollover event. + +.. _ksk_rollover_methods: + +KSK Rollover Methods +++++++++++++++++++++ + +Rolling the KSK requires interaction with the parent zone, so +operationally this may be more complex than rolling ZSKs. There are +three methods of rolling the KSK: + +1. *Double-KSK*: Add the new KSK to the DNSKEY RRset, which is then + signed with both the old and new keys. After waiting for the old RRset + to expire from caches, change the DS record in the parent zone. + After waiting a further TTL interval for this change to be reflected in + caches, remove the old key from the RRset. + + Basically, the new KSK is added first at the child zone and + used to sign the DNSKEY; then the DS record is changed, followed by the + removal of the old KSK. Double-KSK keeps the interaction with the + parent zone to a minimum, but for the duration of the rollover, the + size of the DNSKEY RRset is increased. + +2. *Double-DS*: Publish the new DS record. After waiting for this + change to propagate into caches, change the KSK. After a further TTL + interval during which the old DNSKEY RRset expires from caches, remove the + old DS record. + + Double-DS is the reverse of Double-KSK: the new DS is published at + the parent first, then the KSK at the child is updated, then + the old DS at the parent is removed. The benefit is that the size of the DNSKEY + RRset is kept to a minimum, but interactions with the parent zone are + increased to two events. This is the method described in + :ref:`recipes_ksk_rollover`. + +3. *Double-RRset*: Add the new KSK to the DNSKEY RRset, which is + then signed with both the old and new key, and add the new DS record + to the parent zone. After waiting a suitable interval for the + old DS and DNSKEY RRsets to expire from caches, remove the old DNSKEY and + old DS record. + + Double-RRset is the fastest way to roll the KSK (i.e., it has the shortest rollover + time), but has the drawbacks of both of the other methods: a larger + DNSKEY RRset and two interactions with the parent. + +.. _csk_rollover_methods: + +CSK Rollover Methods +++++++++++++++++++++ + +Rolling the CSK is more complex than rolling either the ZSK or KSK, as +the timing constraints relating to both the parent zone and the caching +of records by downstream recursive servers must be taken into +account. There are numerous possible methods that are a combination of ZSK +rollover and KSK rollover methods. BIND 9 automatic signing uses a +combination of ZSK Pre-Publication and Double-KSK rollover. + +.. _advanced_discussions_emergency_rollovers: + +Emergency Key Rollovers +^^^^^^^^^^^^^^^^^^^^^^^ + +Keys are generally rolled on a regular schedule - if you choose +to roll them at all. But sometimes, you may have to rollover keys +out-of-schedule due to a security incident. The aim of an emergency +rollover is to re-sign the zone with a new key as soon as possible, because +when a key is suspected of being compromised, a malicious attacker (or +anyone who has access to the key) could impersonate your server and trick other +validating resolvers into believing that they are receiving authentic, +validated answers. + +During an emergency rollover, follow the same operational +procedures described in :ref:`recipes_rollovers`, with the added +task of reducing the TTL of the current active (potentially compromised) DNSKEY +RRset, in an attempt to phase out the compromised key faster before the new +key takes effect. The time frame should be significantly reduced from +the 30-days-apart example, since you probably do not want to wait up to +60 days for the compromised key to be removed from your zone. + +Another method is to carry a spare key with you at all times. If +you have a second key pre-published and that one +is not compromised at the same time as the first key, +you could save yourself some time by immediately +activating the spare key if the active +key is compromised. With pre-publication, all validating resolvers should already +have this spare key cached, thus saving you some time. + +With a KSK emergency rollover, you also need to consider factors +related to your parent zone, such as how quickly they can remove the old +DS records and publish the new ones. + +As with many other facets of DNSSEC, there are multiple aspects to take into +account when it comes to emergency key rollovers. For more in-depth +considerations, please check out :rfc:`7583`. + +.. _advanced_discussions_DNSKEY_algorithm_rollovers: + +Algorithm Rollovers +^^^^^^^^^^^^^^^^^^^ + +From time to time, new digital signature algorithms with improved +security are introduced, and it may be desirable for administrators to +roll over DNSKEYs to a new algorithm, e.g., from RSASHA1 (algorithm 5 or +7) to RSASHA256 (algorithm 8). The algorithm rollover steps must be followed with +care to avoid breaking DNSSEC validation. + +If you are managing DNSSEC by using the ``dnssec-policy`` configuration, +``named`` handles the rollover for you. Simply change the algorithm +for the relevant keys, and ``named`` uses the new algorithm when the +key is next rolled. It performs a smooth transition to the new +algorithm, ensuring that the zone remains valid throughout rollover. + +If you are using other methods to sign the zone, the administrator needs to do more work. As +with other key rollovers, when the zone is a primary zone, an algorithm +rollover can be accomplished using dynamic updates or automatic key +rollovers. For secondary zones, only automatic key rollovers are +possible, but the ``dnssec-settime`` utility can be used to control the +timing. + +In any case, the first step is to put DNSKEYs in place using the new algorithm. +You must generate the ``K*`` files for the new algorithm and put +them in the zone's key directory, where ``named`` can access them. Take +care to set appropriate ownership and permissions on the keys. If the +``auto-dnssec`` zone option is set to ``maintain``, ``named`` +automatically signs the zone with the new keys, based on their timing +metadata when the ``dnssec-loadkeys-interval`` elapses or when you issue the +``rndc loadkeys`` command. Otherwise, for primary zones, you can use +``nsupdate`` to add the new DNSKEYs to the zone; this causes ``named`` +to use them to sign the zone. For secondary zones, e.g., on a +"bump in the wire" signing server, ``nsupdate`` cannot be used. + +Once the zone has been signed by the new DNSKEYs (and you have waited +for at least one TTL period), you must inform the parent zone and any trust +anchor repositories of the new KSKs, e.g., you might place DS records in +the parent zone through your DNS registrar's website. + +Before starting to remove the old algorithm from a zone, you must allow +the maximum TTL on its DS records in the parent zone to expire. This +assures that any subsequent queries retrieve the new DS records +for the new algorithm. After the TTL has expired, you can remove the DS +records for the old algorithm from the parent zone and any trust anchor +repositories. You must then allow another maximum TTL interval to elapse +so that the old DS records disappear from all resolver caches. + +The next step is to remove the DNSKEYs using the old algorithm from your +zone. Again this can be accomplished using ``nsupdate`` to delete the +old DNSKEYs (for primary zones only) or by automatic key rollover when +``auto-dnssec`` is set to ``maintain``. You can cause the automatic key +rollover to take place immediately by using the ``dnssec-settime`` +utility to set the *Delete* date on all keys to any time in the past. +(See the ``dnssec-settime -D <date/offset>`` option.) + +After adjusting the timing metadata, the ``rndc loadkeys`` command +causes ``named`` to remove the DNSKEYs and +RRSIGs for the old algorithm from the zone. Note also that with the +``nsupdate`` method, removing the DNSKEYs also causes ``named`` to +remove the associated RRSIGs automatically. + +Once you have verified that the old DNSKEYs and RRSIGs have been removed +from the zone, the final (optional) step is to remove the key files for +the old algorithm from the key directory. + +Other Topics +~~~~~~~~~~~~ + +DNSSEC and Dynamic Updates +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Dynamic DNS (DDNS) is actually independent of DNSSEC. DDNS provides a +mechanism, separate from editing the zone file or zone database, to edit DNS +data. Most DNS clients and servers are able to handle dynamic +updates, and DDNS can also be integrated as part of your DHCP +environment. + +When you have both DNSSEC and dynamic updates in your environment, +updating zone data works the same way as with traditional (insecure) +DNS: you can use ``rndc freeze`` before editing the zone file, and +``rndc thaw`` when you have finished editing, or you can use the +command ``nsupdate`` to add, edit, or remove records like this: + +:: + + $ nsupdate + > server 192.168.1.13 + > update add xyz.example.com. 300 IN A 1.1.1.1 + > send + > quit + +The examples provided in this guide make ``named`` automatically +re-sign the zone whenever its content has changed. If you decide to sign +your own zone file manually, you need to remember to execute the +``dnssec-signzone`` command whenever your zone file has been updated. + +As far as system resources and performance are concerned, be mindful that +with a DNSSEC zone that changes frequently, every time the zone +changes your system is executing a series of cryptographic operations +to (re)generate signatures and NSEC or NSEC3 records. + +.. _dnssec_on_private_networks: + +DNSSEC on Private Networks +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Let's clarify what we mean: in this section, "private networks" really refers to +a private or internal DNS view. Most DNS products offer the ability to +have different versions of DNS answers, depending on the origin of the +query. This feature is often called "DNS views" or "split DNS," and is most +commonly implemented as an "internal" versus an "external" setup. + +For instance, your organization may have a version of ``example.com`` +that is offered to the world, and its names most likely resolve to +publicly reachable IP addresses. You may also have an internal version +of ``example.com`` that is only accessible when you are on the company's +private networks or via a VPN connection. These private networks typically +fall under 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16 for IPv4. + +So what if you want to offer DNSSEC for your internal version of +``example.com``? This can be done: the golden rule is to use the same +key for both the internal and external versions of the zones. This +avoids problems that can occur when machines (e.g., laptops) move +between accessing the internal and external zones, when it is possible +that they may have cached records from the wrong zone. + +.. _introduction_to_dane: + +Introduction to DANE +^^^^^^^^^^^^^^^^^^^^ + +With your DNS infrastructure secured with DNSSEC, information can +now be stored in DNS and its integrity and authenticity can be proved. +One of the new features that takes advantage of this is the DNS-Based +Authentication of Named Entities, or DANE. This improves security in a +number of ways, including: + +- The ability to store self-signed X.509 certificates and bypass having to pay a third + party (such as a Certificate Authority) to sign the certificates + (:rfc:`6698`). + +- Improved security for clients connecting to mail servers (:rfc:`7672`). + +- A secure way of getting public PGP keys (:rfc:`7929`). + +Disadvantages of DNSSEC +~~~~~~~~~~~~~~~~~~~~~~~ + +DNSSEC, like many things in this world, is not without its problems. +Below are a few challenges and disadvantages that DNSSEC faces. + +1. *Increased, well, everything*: With DNSSEC, signed zones are larger, + thus taking up more disk space; for DNSSEC-aware servers, the + additional cryptographic computation usually results in increased + system load; and the network packets are bigger, possibly putting + more strains on the network infrastructure. + +2. *Different security considerations*: DNSSEC addresses many security + concerns, most notably cache poisoning. But at the same time, it may + introduce a set of different security considerations, such as + amplification attack and zone enumeration through NSEC. These + concerns are still being identified and addressed by the Internet + community. + +3. *More complexity*: If you have read this far, you have probably already + concluded this yourself. With additional resource records, keys, + signatures, and rotations, DNSSEC adds many more moving pieces on top of + the existing DNS machine. The job of the DNS administrator changes, + as DNS becomes the new secure repository of everything from spam + avoidance to encryption keys, and the amount of work involved to + troubleshoot a DNS-related issue becomes more challenging. + +4. *Increased fragility*: The increased complexity means more + opportunities for things to go wrong. Before DNSSEC, DNS + was essentially "add something to the zone and forget it." With DNSSEC, + each new component - re-signing, key rollover, interaction with + parent zone, key management - adds more opportunity for error. It is + entirely possible that a failure to validate a name may come down to + errors on the part of one or more zone operators rather than the + result of a deliberate attack on the DNS. + +5. *New maintenance tasks*: Even if your new secure DNS infrastructure + runs without any hiccups or security breaches, it still requires + regular attention, from re-signing to key rollovers. While most of + these can be automated, some of the tasks, such as KSK rollover, + remain manual for the time being. + +6. *Not enough people are using it today*: While it's estimated (as of + mid-2020) that roughly 30% of the global Internet DNS traffic is + validating [#]_ , that doesn't mean that many of the DNS zones are + actually signed. What this means is, even if your company's zone is + signed today, fewer than 30% of the Internet's servers are taking + advantage of this extra security. It gets worse: with less than 1.5% + of the ``com.`` domains signed, even if your DNSSEC validation is enabled today, + it's not likely to buy you or your users a whole lot more protection + until these popular domain names decide to sign their zones. + +The last point may have more impact than you realize. Consider this: +HTTP and HTTPS make up the majority of traffic on the Internet. While you may have +secured your DNS infrastructure through DNSSEC, if your web hosting is +outsourced to a third party that does not yet support DNSSEC in its +own domain, or if your web page loads contents and components from +insecure domains, end users may experience validation problems when +trying to access your web page. For example, although you may have signed +the zone ``company.com``, the web address ``www.company.com`` may actually be a +CNAME to ``foo.random-cloud-provider.com``. As long as +``random-cloud-provider.com`` remains an insecure DNS zone, users cannot +fully validate everything when they visit your web page and could be +redirected elsewhere by a cache poisoning attack. + +.. [#] + Based on APNIC statistics at + `<https://stats.labs.apnic.net/dnssec/XA>`__ diff --git a/doc/dnssec-guide/commonly-asked-questions.rst b/doc/dnssec-guide/commonly-asked-questions.rst new file mode 100644 index 0000000..a506777 --- /dev/null +++ b/doc/dnssec-guide/commonly-asked-questions.rst @@ -0,0 +1,172 @@ +.. Copyright (C) Internet Systems Consortium, Inc. ("ISC") +.. +.. SPDX-License-Identifier: MPL-2.0 +.. +.. This Source Code Form is subject to the terms of the Mozilla Public +.. License, v. 2.0. If a copy of the MPL was not distributed with this +.. file, you can obtain one at https://mozilla.org/MPL/2.0/. +.. +.. See the COPYRIGHT file distributed with this work for additional +.. information regarding copyright ownership. + +.. _dnssec_commonly_asked_questions: + +Commonly Asked Questions +------------------------ + +Below are some common questions and (hopefully) some answers that +help. + +Do I need IPv6 to have DNSSEC? + No. DNSSEC can be deployed without IPv6. + +Does DNSSEC encrypt my DNS traffic, so others cannot eavesdrop on my DNS queries? + No. Although cryptographic keys and digital signatures + are used in DNSSEC, they only provide authenticity and integrity, not + privacy. Someone who sniffs network traffic can still see all the DNS + queries and answers in plain text; DNSSEC just makes it very difficult + for the eavesdropper to alter or spoof the DNS responses. + For protection against eavesdropping, the preferred protocol is DNS-over-TLS. + DNS-over-HTTPS can also do the job, but it is more complex. + +If I deploy DNS-over-TLS/HTTPS, can I skip deploying DNSSEC? + No. DNS-over-encrypted-transport stops eavesdroppers on a network, but it does + not protect against cache poisoning and answer manipulation in other parts + of the DNS resolution chain. In other words, these technologies offer protection + only for records when they are in transit between two machines; any + compromised server can still redirect traffic elsewhere (or simply eavesdrop). + However, DNSSEC provides integrity and authenticity for DNS + *records*, even when these records are stored in caches and on disks. + +Does DNSSEC protect the communication between my laptop and my name server? + Unfortunately, not at the moment. DNSSEC is designed to protect the + communication between end clients (laptop) and name servers; + however, there are few applications or stub resolver libraries as of + mid-2020 that take advantage of this capability. + +Does DNSSEC secure zone transfers? + No. You should consider using TSIG to secure zone transfers among your + name servers. + +Does DNSSEC protect my network from malicious websites? + DNSSEC makes it much more difficult for attackers to spoof DNS responses + or perform cache poisoning. It cannot protect against users who + visit a malicious website that an attacker owns and operates, or prevent users from + mistyping a domain name; it will just become less likely that an attacker can + hijack other domain names. + + In other words, DNSSEC is designed to provide confidence that when + a DNS response is received for www.company.com over port 53, it really came from + Company's name servers and the answers are authentic. But that does not mean + the web server a user visits over port 80 or port 443 is necessarily safe. + +If I enable DNSSEC validation, will it break DNS lookup, since most domain names do not yet use DNSSEC? + No, DNSSEC is backwards-compatible to "standard" DNS. A DNSSEC-enabled + validating resolver can still look up all of these domain names as it always + has under standard DNS. + + There are four (4) categories of responses (see :rfc:`4035`): + + .. glossary:: + + Secure + Domains that have DNSSEC deployed correctly. + + Insecure + Domains that have yet to deploy DNSSEC. + + Bogus + Domains that have deployed DNSSEC but have done it incorrectly. + + Indeterminate + Domains for which it is not possible to determine whether these domains use DNSSEC. + + A DNSSEC-enabled validating resolver still resolves :term:`Secure` and + :term:`Insecure`; only :term:`Bogus` and :term:`Indeterminate` result in a + SERVFAIL. + As of mid-2022, roughly one-third of users worldwide are using DNSSEC validation + on their recursive name servers. Google public DNS (8.8.8.8) also has + enabled DNSSEC validation. + +Do I need to have special client software to use DNSSEC? + No. DNSSEC only changes the communication + behavior among DNS servers, not between a DNS server (validating resolver) and + a client (stub resolver). With DNSSEC validation enabled on your recursive + server, if a domain name does not pass the checks, an error message + (typically SERVFAIL) is returned to clients; to most client + software today, it appears that the DNS query has failed or that the domain + name does not exist. + +Since DNSSEC uses public key cryptography, do I need Public Key Infrastructure (PKI) in order to use DNSSEC? + No, DNSSEC does not depend on an existing PKI. Public keys are stored within + the DNS hierarchy; the trustworthiness of each zone is guaranteed by + its parent zone, all the way back to the root zone. A copy of the trust + anchor for the root zone is distributed with BIND 9. + +Do I need to purchase SSL certificates from a Certificate Authority (CA) to use DNSSEC? + No. With DNSSEC, you generate and publish your own keys, and sign your own + data as well. There is no need to pay someone else to do it for you. + +My parent zone does not support DNSSEC; can I still sign my zone? + Technically, yes, but you will not get + the full benefit of DNSSEC, as other validating resolvers are not + able to validate your zone data. Without the DS record(s) in your parent + zone, other validating resolvers treat your zone as an insecure + (traditional) zone, and no actual verification is carried out. + To the rest of the world, your zone still appears to be + insecure, and it will continue to be insecure until your parent zone can + host the DS record(s) for you and tell the rest of the world + that your zone is signed. + +Is DNSSEC the same thing as TSIG? + No. TSIG is typically used + between primary and secondary name servers to secure zone transfers, + while DNSSEC secures DNS lookup by validating answers. Even if you enable + DNSSEC, zone transfers are still not validated; to + secure the communication between your primary and secondary name + servers, consider setting up TSIG or similar secure channels. + +How are keys copied from primary to secondary server(s)? + DNSSEC uses public cryptography, which results in two types of keys: public and + private. The public keys are part of the zone data, stored as DNSKEY + record types. Thus the public keys are synchronized from primary to + secondary server(s) as part of the zone transfer. The private keys are + not, and should not be, stored anywhere other than secured on the primary server. + See :ref:`advanced_discussions_key_storage` for + more information on key storage options and considerations. + +Can I use the same key for multiple zones? + Yes and no. Good security practice + suggests that you should use unique key pairs for each zone, just as + you should have different passwords for your email account, social + media login, and online banking credentials. On a technical level, it + is completely feasible to reuse a key, but multiple zones are at risk if one key + pair is compromised. However, if you have hundreds or thousands + of zones to administer, a single key pair for all might be + less error-prone to manage. You may choose to use the same approach as + with password management: use unique passwords for your bank accounts and + shopping sites, but use a standard password for your not-very-important + logins. First, categorize your zones: high-value zones (or zones that have + specific key rollover requirements) get their own key pairs, while other, + more "generic" zones can use a single key pair for easier management. Note that + at present (mid-2020), fully automatic signing (using the ``dnssec-policy`` + clause in your ``named`` configuration file) does not support reuse of keys + except when the same zone appears in multiple views (see next question). + To use the same key for multiple zones, sign your + zones using semi-automatic signing. Each zone wishing to use the key + should point to the same key directory. + +How do I sign the different instances of a zone that appears in multiple views? + Add a ``dnssec-policy`` statement to each ``zone`` definition in the + configuration file. To avoid problems when a single computer accesses + different instances of the zone while information is still in its cache + (e.g., a laptop moving from your office to a customer site), you + should sign all instances with the same key. This means setting the + same DNSSEC policy for all instances of the zone, and making sure that the + key directory is the same for all instances of the zone. + +Will there be any problems if I change the DNSSEC policy for a zone? + If you are using fully automatic signing, no. Just change the parameters in the + ``dnssec-policy`` statement and reload the configuration file. ``named`` + makes a smooth transition to the new policy, ensuring that your zone + remains valid at all times. diff --git a/doc/dnssec-guide/getting-started.rst b/doc/dnssec-guide/getting-started.rst new file mode 100644 index 0000000..1b212ff --- /dev/null +++ b/doc/dnssec-guide/getting-started.rst @@ -0,0 +1,147 @@ +.. Copyright (C) Internet Systems Consortium, Inc. ("ISC") +.. +.. SPDX-License-Identifier: MPL-2.0 +.. +.. This Source Code Form is subject to the terms of the Mozilla Public +.. License, v. 2.0. If a copy of the MPL was not distributed with this +.. file, you can obtain one at https://mozilla.org/MPL/2.0/. +.. +.. See the COPYRIGHT file distributed with this work for additional +.. information regarding copyright ownership. + +.. _getting_started: + +Getting Started +--------------- + +.. _software_requirements: + +Software Requirements +~~~~~~~~~~~~~~~~~~~~~ + +This guide assumes BIND 9.16.9 or newer, although the more elaborate manual +procedures do work with all versions of BIND later than 9.9. + +We recommend running the latest stable version to get the most +complete DNSSEC configuration, as well as the latest security fixes. + +.. _hardware_requirements: + +Hardware Requirements +~~~~~~~~~~~~~~~~~~~~~ + +.. _recursive_server_hardware: + +Recursive Server Hardware +^^^^^^^^^^^^^^^^^^^^^^^^^ + +Enabling DNSSEC validation on a recursive server makes it a *validating +resolver*. The job of a validating resolver is to fetch additional +information that can be used to computationally verify the answer set. +Contrary to popular belief, the increase in resource consumption is very modest: + +1. *CPU*: a validating resolver executes cryptographic functions on cache-miss + answers, which leads to increased CPU usage. Thanks to standard DNS caching + and contemporary CPUs, the increase in CPU-time consumption in a steady + state is negligible - typically on the order of 5%. For a brief period (a few + minutes) after the resolver starts, the increase might be as much as 20%, but it + quickly decreases as the DNS cache fills in. + +2. *System memory*: DNSSEC leads to larger answer sets and occupies + more memory space. With typical ISP traffic and the state of the Internet as + of mid-2022, memory consumption for the cache increases by roughly 20%. + +3. *Network interfaces*: although DNSSEC does increase the amount of DNS + traffic overall, in practice this increase is often within measurement + error. + +.. _authoritative_server_hardware: + +Authoritative Server Hardware +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +On the authoritative server side, DNSSEC is enabled on a zone-by-zone +basis. When a zone is DNSSEC-enabled, it is also known as "signed." +Below are the expected changes to resource consumption caused by serving +DNSSEC-signed zones: + +1. *CPU*: a DNSSEC-signed zone requires periodic re-signing, which is a + cryptographic function that is CPU-intensive. If your DNS zone is + dynamic or changes frequently, that also adds to higher CPU loads. + +2. *System storage*: A signed zone is definitely larger than an unsigned + zone. How much larger? See + :ref:`your_zone_before_and_after_dnssec` for a comparison + example. The final size depends on the structure of the zone, the signing algorithm, + the number of keys, the choice of NSEC or NSEC3, the ratio of signed delegations, the zone file + format, etc. Usually, the size of a signed zone ranges from a negligible + increase to as much as three times the size of the unsigned zone. + +3. *System memory*: Larger DNS zone files take up not only more storage + space on the file system, but also more space when they are loaded + into system memory. The final memory consumption also depends on all the + variables listed above: in the typical case the increase is around half of + the unsigned zone memory consumption, but it can be as high as three times + for some corner cases. + +4. *Network interfaces*: While your authoritative name servers will + begin sending back larger responses, it is unlikely that you need to + upgrade your network interface card (NIC) on the name server unless + you have some truly outdated hardware. + +One factor to consider, but over which you really have no control, is +the number of users who query your domain name who themselves have DNSSEC +enabled. As of mid-2022, measurements by `APNIC +<https://stats.labs.apnic.net/dnssec>`__ show 41% of Internet users send +DNSSEC-aware queries. This means that more DNS queries for your domain will +take advantage of the additional security features, which will result in +increased system load and possibly network traffic. + +.. _network_requirements: + +Network Requirements +~~~~~~~~~~~~~~~~~~~~ + +From a network perspective, DNS and DNSSEC packets are very similar; +DNSSEC packets are just bigger, which means DNS is more likely to use +TCP. You should test for the following two items to make sure your +network is ready for DNSSEC: + +1. *DNS over TCP*: Verify network connectivity over TCP port 53, which + may mean updating firewall policies or Access Control Lists (ACL) on + routers. See :ref:`dns_uses_tcp` for more details. + +2. *Large UDP packets*: Some network equipment, such as firewalls, may + make assumptions about the size of DNS UDP packets and incorrectly + reject DNS traffic that appears "too big." Verify that the + responses your name server generates are being seen by the rest of the + world: see :ref:`whats_edns0_all_about` for more details. + +.. _operational_requirements: + +Operational Requirements +~~~~~~~~~~~~~~~~~~~~~~~~ + +.. _parent_zone: + +Parent Zone +^^^^^^^^^^^ + +Before starting your DNSSEC deployment, check with your parent zone +administrators to make sure they support DNSSEC. This may or may not be +the same entity as your registrar. As you will see later in +:ref:`working_with_parent_zone`, a crucial step in DNSSEC deployment +is establishing the parent-child trust relationship. If your parent zone +does not yet support DNSSEC, contact that administrator to voice your concerns. + +.. _security_requirements: + +Security Requirements +^^^^^^^^^^^^^^^^^^^^^ + +Some organizations may be subject to stricter security requirements than +others. Check to see if your organization requires stronger +cryptographic keys be generated and stored, and how often keys need to be +rotated. The examples presented in this document are not intended for +high-value zones. 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Copyright (C) Internet Systems Consortium, Inc. ("ISC") +.. +.. SPDX-License-Identifier: MPL-2.0 +.. +.. This Source Code Form is subject to the terms of the Mozilla Public +.. License, v. 2.0. If a copy of the MPL was not distributed with this +.. file, you can obtain one at https://mozilla.org/MPL/2.0/. +.. +.. See the COPYRIGHT file distributed with this work for additional +.. information regarding copyright ownership. + +.. _dnssec_guide_introduction: + +Introduction +------------ + +.. _who_should_read: + +Who Should Read this Guide? +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +This guide is intended as an introduction to DNSSEC for the DNS +administrator who is already comfortable working with the existing BIND and DNS +infrastructure. He or she might be curious about DNSSEC, but may not have had the +time to investigate DNSSEC, to learn whether DNSSEC should +be a part of his or her environment, and understand what it means to deploy it in the +field. + +This guide provides basic information on how to configure DNSSEC using +BIND 9.16.9 or later. Most of the information and examples in this guide also +apply to versions of BIND later than 9.9.0, but some of the key features described here +were only introduced in version 9.16.9. Readers are assumed to have basic +working knowledge of the Domain Name System (DNS) and related network +infrastructure, such as concepts of TCP/IP. In-depth knowledge of DNS and +TCP/IP is not required. The guide assumes no prior knowledge of DNSSEC or +related technology such as public key cryptography. + +.. _who_should_not_read: + +Who May Not Want to Read this Guide? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +If you are already operating a DNSSEC-signed zone, you may not learn +much from the first half of this document, and you may want to start with +:ref:`dnssec_advanced_discussions`. If you want to +learn about details of the protocol extension, such as data fields and flags, +or the new record types, this document can help you get started but it +does not include all the technical details. + +If you are experienced in DNSSEC, you +may find some of the concepts in this document to be overly simplified for +your taste, and some details are intentionally omitted at times for ease of +illustration. + +If you administer a large or complex BIND environment, this +guide may not provide enough information for you, as it is intended to provide +only basic, generic working examples. + +If you are a top-level domain (TLD) operator, or +administer zones under signed TLDs, this guide can +help you get started, but it does not provide enough details to serve all of your +needs. + +If your DNS environment uses DNS products other than (or in addition to) +BIND, this document may provide some background or overlapping information, but you +should check each product's vendor documentation for specifics. + +Finally, deploying +DNSSEC on internal or private networks is not covered in this document, with the +exception of a brief discussion in :ref:`dnssec_on_private_networks`. + +.. _what_is_dnssec: + +What is DNSSEC? +~~~~~~~~~~~~~~~ + +The Domain Name System (DNS) was designed in a day and age when the +Internet was a friendly and trusting place. The protocol itself provides +little protection against malicious or forged answers. DNS Security +Extensions (DNSSEC) addresses this need, by adding digital signatures +into DNS data so that each DNS response can be verified for integrity +(the answer did not change during transit) and authenticity (the data +came from the true source, not an impostor). In the ideal world, when +DNSSEC is fully deployed, every single DNS answer can be validated and +trusted. + +DNSSEC does not provide a secure tunnel; it does not encrypt or hide DNS +data. It operates independently of an existing Public Key Infrastructure +(PKI). It does not need SSL certificates or shared secrets. It was +designed with backwards compatibility in mind, and can be deployed +without impacting "old" unsecured domain names. + +DNSSEC is deployed on the three major components of the DNS +infrastructure: + +- *Recursive Servers*: People use recursive servers to lookup external + domain names such as ``www.example.com``. Operators of recursive servers + need to enable DNSSEC validation. With validation enabled, recursive + servers carry out additional tasks on each DNS response they + receive to ensure its authenticity. + +- *Authoritative Servers*: People who publish DNS data on their name + servers need to sign that data. This entails creating additional + resource records, and publishing them to parent domains where + necessary. With DNSSEC enabled, authoritative servers respond to + queries with additional DNS data, such as digital signatures and + keys, in addition to the standard answers. + +- *Applications*: This component lives on every client machine, from web + servers to smart phones. This includes resolver libraries on different + operating systems, and applications such as web browsers. + +In this guide, we focus on the first two components, Recursive +Servers and Authoritative Servers, and only lightly touch on the third +component. We look at how DNSSEC works, how to configure a +validating resolver, how to sign DNS zone data, and other operational +tasks and considerations. + +.. _what_does_dnssec_add_to_dns: + +What Does DNSSEC Add to DNS? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +.. note:: + + Public Key Cryptography works on the concept of a pair of keys: one + made available to the world publicly, and one kept in secrecy + privately. Not surprisingly, they are known as a public key and a private + key. If you are not familiar with the concept, think of it as a + cleverly designed lock, where one key locks and one key unlocks. In + DNSSEC, we give out the unlocking public key to the rest of the + world, while keeping the locking key private. To learn how this is + used to secure DNS messages, see :ref:`how_are_answers_verified`. + +DNSSEC introduces eight new resource record types: + +- RRSIG (digital resource record signature) + +- DNSKEY (public key) + +- DS (parent-child) + +- NSEC (proof of nonexistence) + +- NSEC3 (proof of nonexistence) + +- NSEC3PARAM (proof of nonexistence) + +- CDS (child-parent signaling) + +- CDNSKEY (child-parent signaling) + +This guide does not go deep into the anatomy of each resource record +type; the details are left for the reader to research and explore. +Below is a short introduction on each of the new record types: + +- *RRSIG*: With DNSSEC enabled, just about every DNS answer (A, PTR, + MX, SOA, DNSKEY, etc.) comes with at least one resource + record signature, or RRSIG. These signatures are used by recursive name + servers, also known as validating resolvers, to verify the answers + received. To learn how digital signatures are generated and used, see + :ref:`how_are_answers_verified`. + +- *DNSKEY*: DNSSEC relies on public-key cryptography for data + authenticity and integrity. There are several keys used in DNSSEC, + some private, some public. The public keys are published to the world + as part of the zone data, and they are stored in the DNSKEY record + type. + + In general, keys in DNSSEC are used for one or both of the following + roles: as a Zone Signing Key (ZSK), used to protect all zone data; or + as a Key Signing Key (KSK), used to protect the zone's keys. A key + that is used for both roles is referred to as a Combined Signing Key + (CSK). We talk about keys in more detail in + :ref:`advanced_discussions_key_generation`. + +- *DS*: One of the critical components of DNSSEC is that the parent + zone can "vouch" for its child zone. The DS record is verifiable + information (generated from one of the child's public keys) that a + parent zone publishes about its child as part of the chain of trust. + To learn more about the Chain of Trust, see + :ref:`chain_of_trust`. + +- *NSEC, NSEC3, NSEC3PARAM*: These resource records all deal with a + very interesting problem: proving that something does not exist. We + look at these record types in more detail in + :ref:`advanced_discussions_proof_of_nonexistence`. + +- *CDS, CDNSKEY*: The CDS and CDNSKEY resource records apply to + operational matters and are a way to signal to the parent zone that + the DS records it holds for the child zone should be updated. This is + covered in more detail in :ref:`cds_cdnskey`. + +.. _how_does_dnssec_change_dns_lookup: + +How Does DNSSEC Change DNS Lookup? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Traditional (insecure) DNS lookup is simple: a recursive name server +receives a query from a client to lookup a name like ``www.isc.org``. The +recursive name server tracks down the authoritative name server(s) +responsible, sends the query to one of the authoritative name servers, +and waits for it to respond with the answer. + +With DNSSEC validation enabled, a validating recursive name server +(a.k.a. a *validating resolver*) asks for additional resource +records in its query, hoping the remote authoritative name servers +respond with more than just the answer to the query, but some proof to +go along with the answer as well. If DNSSEC responses are received, the +validating resolver performs cryptographic computation to verify the +authenticity (the origin of the data) and integrity (that the data was not altered +during transit) of the answers, and even asks the parent zone as part of +the verification. It repeats this process of get-key, validate, +ask-parent, and its parent, and its parent, all the way until +the validating resolver reaches a key that it trusts. In the ideal, +fully deployed world of DNSSEC, all validating resolvers only need to +trust one key: the root key. + +.. _dnssec_12_steps: + +The 12-Step DNSSEC Validation Process (Simplified) +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The following example shows the 12 steps of the DNSSEC validating process +at a very high level, looking up the name ``www.isc.org`` : + +.. figure:: ../dnssec-guide/img/dnssec-12-steps.png + :alt: DNSSEC Validation 12 Steps + +1. Upon receiving a DNS query from a client to resolve ``www.isc.org``, + the validating resolver follows standard DNS protocol to track down + the name server for ``isc.org``, and sends it a DNS query to ask for the + A record of ``www.isc.org``. But since this is a DNSSEC-enabled + resolver, the outgoing query has a bit set indicating it wants + DNSSEC answers, hoping the name server that receives it is DNSSEC-enabled + and can honor this secure request. + +2. The ``isc.org`` name server is DNSSEC-enabled, so it responds with both + the answer (in this case, an A record) and a digital signature for + verification purposes. + +3. The validating resolver requires cryptographic keys to be able to verify the + digital signature, so it asks the ``isc.org`` name server for those keys. + +4. The ``isc.org`` name server responds with the cryptographic keys + (and digital signatures of the keys) used to generate the digital + signature that was sent in #2. At this point, the validating + resolver can use this information to verify the answers received in + #2. + + Let's take a quick break here and look at what we've got so far... + how can our server trust this answer? If a clever attacker had taken over + the ``isc.org`` name server(s), of course she would send matching + keys and signatures. We need to ask someone else to have confidence + that we are really talking to the real ``isc.org`` name server. This + is a critical part of DNSSEC: at some point, the DNS administrators + at ``isc.org`` uploaded some cryptographic information to its + parent, ``.org``, maybe through a secure web form, maybe + through an email exchange, or perhaps in person. In + any event, at some point some verifiable information about the + child (``isc.org``) was sent to the parent (``.org``) for + safekeeping. + +5. The validating resolver asks the parent (``.org``) for the + verifiable information it keeps on its child, ``isc.org``. + +6. Verifiable information is sent from the ``.org`` server. At this + point, the validating resolver compares this to the answer it received + in #4; if the two of them match, it proves the authenticity of + ``isc.org``. + + Let's examine this process. You might be thinking to yourself, + what if the clever attacker that took over ``isc.org`` also + compromised the ``.org`` servers? Of course all this information + would match! That's why we turn our attention now to the + ``.org`` server, interrogate it for its cryptographic keys, and + move one level up to ``.org``'s parent, root. + +7. The validating resolver asks the ``.org`` authoritative name server for + its cryptographic keys, to verify the answers received in #6. + +8. The ``.org`` name server responds with the answer (in this case, + keys and signatures). At this point, the validating resolver can + verify the answers received in #6. + +9. The validating resolver asks root (``.org``'s parent) for the verifiable + information it keeps on its child, ``.org``. + +10. The root name server sends back the verifiable information it keeps + on ``.org``. The validating resolver uses this information + to verify the answers received in #8. + + So at this point, both ``isc.org`` and ``.org`` check out. But + what about root? What if this attacker is really clever and somehow + tricked us into thinking she's the root name server? Of course she + would send us all matching information! So we repeat the + interrogation process and ask for the keys from the root name + server. + +11. The validating resolver asks the root name server for its cryptographic + keys to verify the answer(s) received in #10. + +12. The root name server sends its keys; at this point, the validating + resolver can verify the answer(s) received in #10. + +.. _chain_of_trust: + +Chain of Trust +^^^^^^^^^^^^^^ + +But what about the root server itself? Who do we go to verify root's +keys? There's no parent zone for root. In security, you have to trust +someone, and in the perfectly protected world of DNSSEC (we talk later +about the current imperfect state and ways to work around it), +each validating resolver would only have to trust one entity, that is, +the root name server. The validating resolver already has the root key +on file (we discuss later how we got the root key file). So +after the answer in #12 is received, the validating resolver compares it +to the key it already has on file. Providing one of the keys in the +answer matches the one on file, we can trust the answer from root. Thus +we can trust ``.org``, and thus we can trust ``isc.org``. This is known +as the "chain of trust" in DNSSEC. + +We revisit this 12-step process again later in +:ref:`how_does_dnssec_change_dns_lookup_revisited` with more +technical details. + +.. _why_is_dnssec_important: + +Why is DNSSEC Important? (Why Should I Care?) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +You might be thinking to yourself: all this DNSSEC stuff sounds +wonderful, but why should I care? Below are some reasons why you may +want to consider deploying DNSSEC: + +1. *Being a good netizen*: By enabling DNSSEC validation (as described in + :ref:`dnssec_validation`) on your DNS servers, you're protecting + your users and yourself a little more by checking answers returned to + you; by signing your zones (as described in + :ref:`dnssec_signing`), you are making it possible for other + people to verify your zone data. As more people adopt DNSSEC, the + Internet as a whole becomes more secure for everyone. + +2. *Compliance*: You may not even get a say in + implementing DNSSEC, if your organization is subject to compliance + standards that mandate it. For example, the US government set a + deadline in 2008 to have all ``.gov`` subdomains signed by + December 2009 [#]_. So if you operate a subdomain in ``.gov``, you + must implement DNSSEC to be compliant. ICANN also requires + that all new top-level domains support DNSSEC. + +3. *Enhanced Security*: Okay, so the big lofty goal of "let's be good" + doesn't appeal to you, and you don't have any compliance standards to + worry about. Here is a more practical reason why you should consider + DNSSEC: in the event of a DNS-based security breach, such as cache + poisoning or domain hijacking, after all the financial and brand + damage done to your domain name, you might be placed under scrutiny + for any preventive measure that could have been put in place. Think + of this like having your website only available via HTTP but not + HTTPS. + +4. *New Features*: DNSSEC brings not only enhanced security, but also + a whole new suite of features. Once DNS + can be trusted completely, it becomes possible to publish SSL + certificates in DNS, or PGP keys for fully automatic cross-platform + email encryption, or SSH fingerprints.... New features are still + being developed, but they all rely on a trustworthy DNS + infrastructure. To take a peek at these next-generation DNS features, + check out :ref:`introduction_to_dane`. + +.. [#] + The Office of Management and Budget (OMB) for the US government + published `a memo in + 2008 <https://www.whitehouse.gov/sites/whitehouse.gov/files/omb/memoranda/2008/m08-23.pdf>`__, + requesting all ``.gov`` subdomains to be DNSSEC-signed by December + 2009. This explains why ``.gov`` is the most-deployed DNSSEC domain + currently, with `around 90% of subdomains + signed. <https://fedv6-deployment.antd.nist.gov/cgi-bin/generate-gov>`__ + +.. _how_does_dnssec_change_my_job: + +How Does DNSSEC Change My Job as a DNS Administrator? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +With this protocol extension, some of the things you were used to in DNS +have changed. As the DNS administrator, you have new maintenance +tasks to perform on a regular basis (as described in +:ref:`signing_maintenance_tasks`); when there is a DNS resolution +problem, you have new troubleshooting techniques and tools to use (as +described in :ref:`dnssec_troubleshooting`). BIND 9 tries its best to +make these things as transparent and seamless as possible. In this +guide, we try to use configuration examples that result in the least +amount of work for BIND 9 DNS administrators. diff --git a/doc/dnssec-guide/preface.rst b/doc/dnssec-guide/preface.rst new file mode 100644 index 0000000..13ba820 --- /dev/null +++ b/doc/dnssec-guide/preface.rst @@ -0,0 +1,83 @@ +.. Copyright (C) Internet Systems Consortium, Inc. ("ISC") +.. +.. SPDX-License-Identifier: MPL-2.0 +.. +.. This Source Code Form is subject to the terms of the Mozilla Public +.. License, v. 2.0. If a copy of the MPL was not distributed with this +.. file, you can obtain one at https://mozilla.org/MPL/2.0/. +.. +.. See the COPYRIGHT file distributed with this work for additional +.. information regarding copyright ownership. + +Preface +------- + +.. _preface_organization: + +Organization +~~~~~~~~~~~~ + +This document provides introductory information on how DNSSEC works, how +to configure BIND 9 to support some common DNSSEC features, and +some basic troubleshooting tips. The chapters are organized as follows: + +:ref:`dnssec_guide_introduction` covers the intended audience for this +document, assumed background knowledge, and a basic introduction to the +topic of DNSSEC. + +:ref:`getting_started` covers various requirements +before implementing DNSSEC, such as software versions, hardware +capacity, network requirements, and security changes. + +:ref:`dnssec_validation` walks through setting up a validating +resolver, and gives both more information on the validation process and +some examples of tools to verify that the resolver is properly validating +answers. + +:ref:`dnssec_signing` explains how to set up a basic signed +authoritative zone, details the relationship between a child and a parent zone, +and discusses ongoing maintenance tasks. + +:ref:`dnssec_troubleshooting` provides some tips on how to analyze +and diagnose DNSSEC-related problems. + +:ref:`dnssec_advanced_discussions` covers several topics, including key +generation, key storage, key management, NSEC and NSEC3, and some +disadvantages of DNSSEC. + +:ref:`dnssec_recipes` provides several working examples of common DNSSEC +solutions, with step-by-step details. + +:ref:`dnssec_commonly_asked_questions` lists some commonly asked +questions and answers about DNSSEC. + +.. _preface_acknowledgement: + +Acknowledgements +~~~~~~~~~~~~~~~~ + +This document was originally authored by Josh Kuo of `DeepDive +Networking <https://www.deepdivenetworking.com/>`__. He can be reached +at josh.kuo@gmail.com. + +Thanks to the following individuals (in no particular order) who have +helped in completing this document: Jeremy C. Reed, Heidi Schempf, +Stephen Morris, Jeff Osborn, Vicky Risk, Jim Martin, Evan Hunt, Mark +Andrews, Michael McNally, Kelli Blucher, Chuck Aurora, Francis Dupont, +Rob Nagy, Ray Bellis, Matthijs Mekking, and Suzanne Goldlust. + +Special thanks goes to Cricket Liu and Matt Larson for their +selflessness in knowledge sharing. + +Thanks to all the reviewers and contributors, including John Allen, Jim +Young, Tony Finch, Timothe Litt, and Dr. Jeffry A. Spain. + +The sections on key rollover and key timing metadata borrowed heavily +from the Internet Engineering Task Force draft titled "DNSSEC Key Timing +Considerations" by S. Morris, J. Ihren, J. Dickinson, and W. Mekking, +subsequently published as :rfc:`7583`. + +Icons made by `Freepik <https://www.freepik.com/>`__ and +`SimpleIcon <https://www.simpleicon.com/>`__ from +`Flaticon <https://www.flaticon.com/>`__, licensed under `Creative Commons BY +3.0 <https://creativecommons.org/licenses/by/3.0/>`__. diff --git a/doc/dnssec-guide/recipes.rst b/doc/dnssec-guide/recipes.rst new file mode 100644 index 0000000..a4bdffa --- /dev/null +++ b/doc/dnssec-guide/recipes.rst @@ -0,0 +1,1084 @@ +.. Copyright (C) Internet Systems Consortium, Inc. ("ISC") +.. +.. SPDX-License-Identifier: MPL-2.0 +.. +.. This Source Code Form is subject to the terms of the Mozilla Public +.. License, v. 2.0. If a copy of the MPL was not distributed with this +.. file, you can obtain one at https://mozilla.org/MPL/2.0/. +.. +.. See the COPYRIGHT file distributed with this work for additional +.. information regarding copyright ownership. + +.. _dnssec_recipes: + +Recipes +------- + +This chapter provides step-by-step "recipes" for some common +DNSSEC configurations. + +.. _recipes_inline_signing: + +DNSSEC Signing +~~~~~~~~~~~~~~ + +There are two recipes here: the first shows an example using DNSSEC +signing on the primary server, which has been covered in this +guide; the second shows how to setup a "bump in the +wire" between a hidden primary and the secondary servers to seamlessly +sign the zone "on the fly." + +.. _recipes_inline_signing_primary: + +Primary Server DNSSEC Signing +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +In this recipe, our servers are illustrated as shown in +:ref:`dnssec-signing-1`: we have a primary server +(192.168.1.1) and three secondary servers (192.168.1.2, 192.168.1.3, and +192.168.1.4) that receive zone transfers. To get the zone +signed, we need to reconfigure the primary server. Once reconfigured, a +signed version of the zone is generated on the fly; +zone transfers take care of synchronizing the signed zone data +to all secondary name servers, without configuration or software changes +on them. + +.. _dnssec-signing-1: + +.. figure:: ../dnssec-guide/img/dnssec-inline-signing-1.png + :alt: DNSSEC Signing Recipe #1 + :width: 80.0% + + DNSSEC Signing Recipe #1 + +Using the method described in +:ref:`easy_start_guide_for_authoritative_servers`, we just need to +add a ``dnssec-policy`` statement to the relevant zone clause. This is +what the ``named.conf`` zone statement looks like on the primary server, 192.168.1.1: + +:: + + zone "example.com" IN { + type primary; + file "db/example.com.db"; + key-directory "keys/example.com"; + dnssec-policy default; + inline-signing yes; + allow-transfer { 192.168.1.2; 192.168.1.3; 192.168.1.4; }; + }; + +We have chosen to use the default policy, storing the keys generated for +the zone in the directory ``keys/example.com``. To use a +custom policy, define the policy in the configuration +file and select it in the zone statement (as described in +:ref:`signing_custom_policy`). + +On the secondary servers, ``named.conf`` does not need to be updated, +and it looks like this: + +:: + + zone "example.com" IN { + type secondary; + file "db/example.com.db"; + primaries { 192.168.1.1; }; + }; + +In fact, the secondary servers do not even need to be running BIND; they +can run any DNS product that supports DNSSEC. + +.. _recipes_inline_signing_bump_in_the_wire: + +"Bump in the Wire" Signing +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +In this recipe, we take advantage of the power of automated signing +by placing an additional name server (192.168.1.5) between the hidden +primary (192.168.1.1) and the DNS secondaries (192.168.1.2, 192.168.1.3, +and 192.168.1.4). The additional name server, 192.168.1.5, acts as a "bump +in the wire," taking an unsigned zone from the hidden primary, +and sending out signed data on the other end to the secondary name +servers. The steps described in this recipe may be used as part of a +DNSSEC deployment strategy, since it requires only minimal changes made to +the existing hidden DNS primary and DNS secondaries. + +.. _dnssec-signing-2: + +.. figure:: ../dnssec-guide/img/dnssec-inline-signing-2.png + :alt: DNSSEC Signing Recipe #2 + :width: 100.0% + + DNSSEC Signing Recipe #2 + +It is important to remember that 192.168.1.1 in this case is a hidden +primary not exposed to the world, and it must not be listed in the NS RRset. +Otherwise the world will get conflicting answers: unsigned answers from +the hidden primary and signed answers from the other name servers. + +The only configuration change needed on the hidden primary, 192.168.1.1, +is to make sure it allows our middle box to perform a zone transfer: + +:: + + zone "example.com" IN { + ... + allow-transfer { 192.168.1.5; }; + ... + }; + +On the middle box, 192.168.1.5, all the tasks described in +:ref:`easy_start_guide_for_authoritative_servers` still need to be +performed, such as generating key pairs and uploading information to +the parent zone. This server is configured as secondary to the hidden +primary 192.168.1.1 to receive the unsigned data; then, using keys +accessible to this middle box, to sign data on the fly; and finally, to send out the +signed data via zone transfer to the other three DNS secondaries. Its +``named.conf`` zone statement looks like this: + +:: + + zone example.com { + type secondary; + primaries { 192.168.1.1; }; + file "db/example.com.db"; + key-directory "keys/example.com"; + dnssec-policy default; + inline-signing yes; + allow-transfer { 192.168.1.2; 192.168.1.3; 192.168.1.4; }; + }; + +(As before, the default policy has been selected here. See +:ref:`signing_custom_policy` for instructions on how to define +and use a custom policy.) + +Finally, on the three secondary servers, the configuration should be updated +to receive a zone transfer from 192.168.1.5 (the middle box) instead of +from 192.168.1.1 (the hidden primary). If using BIND, the ``named.conf`` file looks +like this: + +:: + + zone "example.com" IN { + type secondary; + file "db/example.com.db"; + primaries { 192.168.1.5; }; # this was 192.168.1.1 before! + }; + +.. _recipes_rollovers: + +Rollovers +~~~~~~~~~ + +If you are signing your zone using a ``dnssec-policy`` statement, this +section is not really relevant to you. In the policy statement, you set how long +you want your keys to be valid for, the time +taken for information to propagate through your zone, the time it takes +for your parent zone to register a new DS record, etc., and that's more +or less it. ``named`` implements everything for you automatically, apart from +uploading the new DS records to your parent zone - which is covered in +:ref:`signing_easy_start_upload_to_parent_zone`. (Some +screenshots from a session where a KSK is uploaded to the parent zone +are presented here for convenience.) However, these recipes may be useful +in describing what happens +through the rollover process and what you should be monitoring. + +.. _recipes_zsk_rollover: + +ZSK Rollover +^^^^^^^^^^^^ + +This recipe covers how to perform a ZSK rollover using what is known as +the Pre-Publication method. For other ZSK rolling methods, please see +:ref:`zsk_rollover_methods` in :ref:`dnssec_advanced_discussions`. + +Below is a sample timeline for a ZSK rollover to occur on January 1, 2021: + +1. December 1, 2020 (one month before rollover) + + - Generate new ZSK + + - Add DNSKEY for new ZSK to zone + +2. January 1, 2021 (day of rollover) + + - New ZSK used to replace RRSIGs for the bulk of the zone + +3. February 1, 2021 (one month after rollover) + + - Remove old ZSK DNSKEY RRset from zone + + - DNSKEY signatures made with KSK are changed + +The current active ZSK has the ID 17694 in the example below. For more +information on key management and rollovers, please see +:ref:`advanced_discussions_key_management`. + +One Month Before ZSK Rollover ++++++++++++++++++++++++++++++ + +On December 1, 2020, a month before the example rollover, you (as administrator) +should change the parameters on the current key (17694). Set it to become inactive on +January 1, 2021 and be deleted from the zone on February 1, 2021; also, +generate a successor key (51623): + +:: + + # cd /etc/bind/keys/example.com/ + # dnssec-settime -I 20210101 -D 20210201 Kexample.com.+008+17694 + ./Kexample.com.+008+17694.key/GoDaddy + + ./Kexample.com.+008+17694.private + # dnssec-keygen -S Kexample.com.+008+17694 + Generating key pair..++++++ ...........++++++ + Kexample.com.+008+51623 + +The first command gets us into the key directory +``/etc/bind/keys/example.com/``, where keys for ``example.com`` are +stored. + +The second, ``dnssec-settime``, sets an inactive (``-I``) date of January 1, +2021, and a deletion (``-D``) date of February 1, 2021, for the current ZSK +(``Kexample.com.+008+17694``). + +The third command, ``dnssec-keygen``, creates a successor key, using +the exact same parameters (algorithms, key sizes, etc.) as the current +ZSK. The new ZSK created in our example is ``Kexample.com.+008+51623``. + +Make sure the successor keys are readable by ``named``. + +``named``'s logging messages indicate when the next +key checking event is scheduled to occur, the frequency of which can be +controlled by ``dnssec-loadkeys-interval``. The log message looks like +this: + +:: + + zone example.com/IN (signed): next key event: 01-Dec-2020 00:13:05.385 + +And you can check the publish date of the key by looking at the key +file: + +:: + + # cd /etc/bind/keys/example.com + # cat Kexample.com.+008+51623.key + ; This is a zone-signing key, keyid 11623, for example.com. + ; Created: 20201130160024 (Mon Dec 1 00:00:24 2020) + ; Publish: 20201202000000 (Fri Dec 2 08:00:00 2020) + ; Activate: 20210101000000 (Sun Jan 1 08:00:00 2021) + ... + +Since the publish date is set to the morning of December 2, and our example +scenario takes place on December 1, the next +morning you will notice that your zone has gained a new DNSKEY record, +but the new ZSK is not yet being used to generate signatures. Below is +the abbreviated output - with shortened DNSKEY and RRSIG - when querying the +authoritative name server, 192.168.1.13: + +:: + + $ dig @192.168.1.13 example.com. DNSKEY +dnssec +multiline + + ... + ;; ANSWER SECTION: + example.com. 600 IN DNSKEY 257 3 8 ( + AwEAAcWDps...lM3NRn/G/R + ) ; KSK; alg = RSASHA256; key id = 6817 + example.com. 600 IN DNSKEY 256 3 8 ( + AwEAAbi6Vo...qBW5+iAqNz + ) ; ZSK; alg = RSASHA256; key id = 51623 + example.com. 600 IN DNSKEY 256 3 8 ( + AwEAAcjGaU...0rzuu55If5 + ) ; ZSK; alg = RSASHA256; key id = 17694 + example.com. 600 IN RRSIG DNSKEY 8 2 600 ( + 20210101000000 20201201230000 6817 example.com. + LAiaJM26T7...FU9syh/TQ= ) + example.com. 600 IN RRSIG DNSKEY 8 2 600 ( + 20210101000000 20201201230000 17694 example.com. + HK4EBbbOpj...n5V6nvAkI= ) + ... + +For good measure, let's take a look at the SOA record and its +signature for this zone. Notice the RRSIG is signed by the current ZSK, +17694. This will come in handy later when you want to verify whether +the new ZSK is in effect: + +:: + + $ dig @192.168.1.13 example.com. SOA +dnssec +multiline + + ... + ;; ANSWER SECTION: + example.com. 600 IN SOA ns1.example.com. admin.example.com. ( + 2020120102 ; serial + 1800 ; refresh (30 minutes) + 900 ; retry (15 minutes) + 2419200 ; expire (4 weeks) + 300 ; minimum (5 minutes) + ) + example.com. 600 IN RRSIG SOA 8 2 600 ( + 20201230160109 20201130150109 17694 example.com. + YUTC8rFULaWbW+nAHzbfGwNqzARHevpryzRIJMvZBYPo + NAeejNk9saNAoCYKWxGJ0YBc2k+r5fYq1Mg4ll2JkBF5 + buAsAYLw8vEOIxVpXwlArY+oSp9T1w2wfTZ0vhVIxaYX + 6dkcz4I3wbDx2xmG0yngtA6A8lAchERx2EGy0RM= ) + +These are all the manual tasks you need to perform for a ZSK rollover. +If you have followed the configuration examples in this guide of using +``inline-signing`` and ``auto-dnssec``, everything else is automated for +you by BIND. + +Day of ZSK Rollover ++++++++++++++++++++ + +On the actual day of the rollover, although there is technically nothing +for you to do, you should still keep an eye on the zone to make sure new +signatures are being generated by the new ZSK (51623 in this example). +The easiest way is to query the authoritative name server 192.168.1.13 +for the SOA record as you did a month ago: + +:: + + $ dig @192.168.1.13 example.com. SOA +dnssec +multiline + + ... + ;; ANSWER SECTION: + example.com. 600 IN SOA ns1.example.com. admin.example.com. ( + 2020112011 ; serial + 1800 ; refresh (30 minutes) + 900 ; retry (15 minutes) + 2419200 ; expire (4 weeks) + 300 ; minimum (5 minutes) + ) + example.com. 600 IN RRSIG SOA 8 2 600 ( + 20210131000000 20201231230000 51623 example.com. + J4RMNpJPOmMidElyBugJp0RLqXoNqfvo/2AT6yAAvx9X + zZRL1cuhkRcyCSLZ9Z+zZ2y4u2lvQGrNiondaKdQCor7 + uTqH5WCPoqalOCBjqU7c7vlAM27O9RD11nzPNpVQ7xPs + y5nkGqf83OXTK26IfnjU1jqiUKSzg6QR7+XpLk0= ) + ... + +As you can see, the signature generated by the old ZSK (17694) has +disappeared, replaced by a new signature generated from the new ZSK +(51623). + +.. note:: + + Not all signatures will disappear magically on the same day; + it depends on when each one was generated. In the worst-case scenario, + a new signature could have been signed by the old ZSK (17694) moments + before it was deactivated, meaning that the signature could live for almost + 30 more days, until just before February 1. + + This is why it is important to keep the old ZSK in the + zone and not delete it right away. + +One Month After ZSK Rollover +++++++++++++++++++++++++++++ + +Again, technically there is nothing you need to do on this day, +but it doesn't hurt to verify that the old ZSK (17694) is now completely +gone from your zone. ``named`` will not touch +``Kexample.com.+008+17694.private`` and ``Kexample.com.+008+17694.key`` +on your file system. Running the same ``dig`` command for DNSKEY should +suffice: + +:: + + $ dig @192.168.1.13 example.com. DNSKEY +multiline +dnssec + + ... + ;; ANSWER SECTION: + example.com. 600 IN DNSKEY 257 3 8 ( + AwEAAcWDps...lM3NRn/G/R + ) ; KSK; alg = RSASHA256; key id = 6817 + example.com. 600 IN DNSKEY 256 3 8 ( + AwEAAdeCGr...1DnEfX+Xzn + ) ; ZSK; alg = RSASHA256; key id = 51623 + example.com. 600 IN RRSIG DNSKEY 8 2 600 ( + 20170203000000 20170102230000 6817 example.com. + KHY8P0zE21...Y3szrmjAM= ) + example.com. 600 IN RRSIG DNSKEY 8 2 600 ( + 20170203000000 20170102230000 51623 example.com. + G2g3crN17h...Oe4gw6gH8= ) + ... + +Congratulations, the ZSK rollover is complete! As for the actual key +files (the files ending in ``.key`` and ``.private``), they may be deleted at this +point, but they do not have to be. + +.. _recipes_ksk_rollover: + +KSK Rollover +^^^^^^^^^^^^ + +This recipe describes how to perform KSK rollover using the Double-DS +method. For other KSK rolling methods, please see +:ref:`ksk_rollover_methods` in +:ref:`dnssec_advanced_discussions`. The registrar used in this +recipe is `GoDaddy <https://www.godaddy.com>`__. Also for this recipe, +we are keeping the number of DS records down to just one per active set +using just SHA-1, for the sake of better clarity, although in practice +most zone operators choose to upload two DS records as shown in +:ref:`working_with_parent_zone`. For more information on key +management and rollovers, +please see :ref:`advanced_discussions_key_management`. + +Below is a sample timeline for a KSK rollover to occur on January 1, 2021: + +1. December 1, 2020 (one month before rollover) + + - Change timer on the current KSK + + - Generate new KSK and DS records + + - Add DNSKEY for the new KSK to zone + + - Upload new DS records to parent zone + +2. January 1, 2021 (day of rollover) + + - Use the new KSK to sign all DNSKEY RRsets, which generates new + RRSIGs + + - Add new RRSIGs to the zone + + - Remove RRSIG for the old ZSK from zone + + - Start using the new KSK to sign DNSKEY + +3. February 1, 2021 (one month after rollover) + + - Remove the old KSK DNSKEY from zone + + - Remove old DS records from parent zone + +The current active KSK has the ID 24828, and this is the DS record that +has already been published by the parent zone: + +:: + + # dnssec-dsfromkey -a SHA-1 Kexample.com.+007+24828.key + example.com. IN DS 24828 7 1 D4A33E8DD550A9567B4C4971A34AD6C4B80A6AD3 + +.. _one_month_before_ksk_rollover: + +One Month Before KSK Rollover ++++++++++++++++++++++++++++++ + +On December 1, 2020, a month before the planned rollover, you (as +administrator) should +change the parameters on the current key. Set it to become inactive on January +1, 2021, and be deleted from the zone on February 1st, 2021; +also generate a successor key (23550). Finally, generate a new +DS record based on the new key, 23550: + +:: + + # cd /etc/bind/keys/example.com/ + # dnssec-settime -I 20210101 -D 20210201 Kexample.com.+007+24828 + ./Kexample.com.+007+24848.key + ./Kexample.com.+007+24848.private + # dnssec-keygen -S Kexample.com.+007+24848 + Generating key pair.......................................................................................++ ...................................++ + Kexample.com.+007+23550 + # dnssec-dsfromkey -a SHA-1 Kexample.com.+007+23550.key + example.com. IN DS 23550 7 1 54FCF030AA1C79C0088FDEC1BD1C37DAA2E70DFB + +The first command gets us into the key directory +``/etc/bind/keys/example.com/``, where keys for ``example.com`` are +stored. + +The second, ``dnssec-settime``, sets an inactive (``-I``) date of January 1, +2021, and a deletion (``-D``) date of February 1, 2021 for the current KSK +(``Kexample.com.+007+24848``). + +The third command, ``dnssec-keygen``, creates a successor key, using +the exact same parameters (algorithms, key sizes, etc.) as the current +KSK. The new key pair created in our example is ``Kexample.com.+007+23550``. + +The fourth and final command, ``dnssec-dsfromkey``, creates a DS record +from the new KSK (23550), using SHA-1 as the digest type. Again, in +practice most people generate two DS records for both supported digest +types (SHA-1 and SHA-256), but for our example here we are only using +one to keep the output small and hopefully clearer. + +Make sure the successor keys are readable by ``named``. + +The ``syslog`` message indicates when the next key +checking event is. The log message looks like this: + +:: + + zone example.com/IN (signed): next key event: 01-Dec-2020 00:13:05.385 + +You can check the publish date of the key by looking at the key +file: + +:: + + # cd /etc/bind/keys/example.com + # cat Kexample.com.+007+23550.key + ; This is a key-signing key, keyid 23550, for example.com. + ; Created: 20201130160024 (Thu Dec 1 00:00:24 2020) + ; Publish: 20201202000000 (Fri Dec 2 08:00:00 2020) + ; Activate: 20210101000000 (Sun Jan 1 08:00:00 2021) + ... + +Since the publish date is set to the morning of December 2, and our example +scenario takes place on December 1, the next +morning you will notice that your zone has gained a new DNSKEY record +based on your new KSK, but with no corresponding RRSIG yet. Below is the +abbreviated output - with shortened DNSKEY and RRSIG - when querying the +authoritative name server, 192.168.1.13: + +:: + + $ dig @192.168.1.13 example.com. DNSKEY +dnssec +multiline + + ... + ;; ANSWER SECTION: + example.com. 300 IN DNSKEY 256 3 7 ( + AwEAAdYqAc...TiSlrma6Ef + ) ; ZSK; alg = NSEC3RSASHA1; key id = 29747 + example.com. 300 IN DNSKEY 257 3 7 ( + AwEAAeTJ+w...O+Zy9j0m63 + ) ; KSK; alg = NSEC3RSASHA1; key id = 24828 + example.com. 300 IN DNSKEY 257 3 7 ( + AwEAAc1BQN...Wdc0qoH21H + ) ; KSK; alg = NSEC3RSASHA1; key id = 23550 + example.com. 300 IN RRSIG DNSKEY 7 2 300 ( + 20201206125617 20201107115617 24828 example.com. + 4y1iPVJOrK...aC3iF9vgc= ) + example.com. 300 IN RRSIG DNSKEY 7 2 300 ( + 20201206125617 20201107115617 29747 example.com. + g/gfmPjr+y...rt/S/xjPo= ) + + ... + +Anytime after generating the DS record, you can upload it; +it is not necessary to wait for the DNSKEY to be published in your zone, +since this new KSK is not active yet. You can do it +immediately after the new DS record has been generated on December 1, +or you can wait until the next day after you have verified that the +new DNSKEY record is added to the zone. Below are some screenshots from +GoDaddy's web-based interface, used to add a new DS record [#]_. + +1. After logging in, click the green "Launch" button next to the domain + name you want to manage. + + .. _add-ds-1: + + .. figure:: ../dnssec-guide/img/add-ds-1.png + :alt: Upload DS Record Step #1 + :width: 70.0% + + Upload DS Record Step #1 + +2. Scroll down to the "DS Records" section and click "Manage." + + .. _add-ds-2: + + .. figure:: ../dnssec-guide/img/add-ds-2.png + :alt: Upload DS Record Step #2 + :width: 40.0% + + Upload DS Record Step #2 + +3. A dialog appears, displaying the current key (24828). Click "Add DS + Record." + + .. _add-ds-3: + + .. figure:: ../dnssec-guide/img/add-ds-3.png + :alt: Upload DS Record Step #3 + :width: 80.0% + + Upload DS Record Step #3 + +4. Enter the Key ID, algorithm, digest type, and the digest, then click + "Next." + + .. _add-ds-4: + + .. figure:: ../dnssec-guide/img/add-ds-4.png + :alt: Upload DS Record Step #4 + :width: 80.0% + + Upload DS Record Step #4 + +5. Address any errors and click "Finish." + + .. _add-ds-5: + + .. figure:: ../dnssec-guide/img/add-ds-5.png + :alt: Upload DS Record Step #5 + :width: 80.0% + + Upload DS Record Step #5 + +6. Both DS records are shown. Click "Save." + + .. _add-ds-6: + + .. figure:: ../dnssec-guide/img/add-ds-6.png + :alt: Upload DS Record Step #6 + :width: 80.0% + + Upload DS Record Step #6 + +Finally, let's verify that the registrar has published the new DS +record. This may take anywhere from a few minutes to a few days, +depending on your parent zone. You can verify whether your +parent zone has published the new DS record by querying for the DS +record of your zone. In the example below, the Google public DNS server +8.8.8.8 is used: + +:: + + $ dig @8.8.8.8 example.com. DS + + ... + ;; ANSWER SECTION: + example.com. 21552 IN DS 24828 7 1 D4A33E8DD550A9567B4C4971A34AD6C4B80A6AD3 + example.com. 21552 IN DS 23550 7 1 54FCF030AA1C79C0088FDEC1BD1C37DAA2E70DFB + +You can also query your parent zone's authoritative name servers +directly to see if these records have been published. DS records will +not show up on your own authoritative zone, so you cannot query your own +name servers for them. In this recipe, the parent zone is ``.com``, so +querying a few of the ``.com`` name servers is another appropriate +verification. + +Day of KSK Rollover ++++++++++++++++++++ + +If you have followed the examples in this document, as described in +:ref:`easy_start_guide_for_authoritative_servers`, there is +technically nothing you need to do manually on the actual day of the +rollover. However, you should still keep an eye on the zone to make sure +new signature(s) are being generated by the new KSK (23550 in this +example). The easiest way is to query the authoritative name server +192.168.1.13 for the same DNSKEY and signatures, as you did a month +ago: + +:: + + $ dig @192.168.1.13 example.com. DNSKEY +dnssec +multiline + + ... + ;; ANSWER SECTION: + example.com. 300 IN DNSKEY 256 3 7 ( + AwEAAdYqAc...TiSlrma6Ef + ) ; ZSK; alg = NSEC3RSASHA1; key id = 29747 + example.com. 300 IN DNSKEY 257 3 7 ( + AwEAAeTJ+w...O+Zy9j0m63 + ) ; KSK; alg = NSEC3RSASHA1; key id = 24828 + example.com. 300 IN DNSKEY 257 3 7 ( + AwEAAc1BQN...Wdc0qoH21H + ) ; KSK; alg = NSEC3RSASHA1; key id = 23550 + example.com. 300 IN RRSIG DNSKEY 7 2 300 ( + 20210201074900 20210101064900 23550 mydnssecgood.org. + S6zTbBTfvU...Ib5eXkbtE= ) + example.com. 300 IN RRSIG DNSKEY 7 2 300 ( + 20210105074900 20201206064900 29747 mydnssecgood.org. + VY5URQA2/d...OVKr1+KX8= ) + ... + +As you can see, the signature generated by the old KSK (24828) has +disappeared, replaced by a new signature generated from the new KSK +(23550). + +One Month After KSK Rollover +++++++++++++++++++++++++++++ + +While the removal of the old DNSKEY from the zone should be automated by +``named``, the removal of the DS record is manual. You should make sure +the old DNSKEY record is gone from your zone first, by querying for the +DNSKEY records of the zone; this time we expect not to see +the key with an ID of 24828: + +:: + + $ dig @192.168.1.13 example.com. DNSKEY +dnssec +multiline + + ... + ;; ANSWER SECTION: + example.com. 300 IN DNSKEY 256 3 7 ( + AwEAAdYqAc...TiSlrma6Ef + ) ; ZSK; alg = NSEC3RSASHA1; key id = 29747 + example.com. 300 IN DNSKEY 257 3 7 ( + AwEAAc1BQN...Wdc0qoH21H + ) ; KSK; alg = NSEC3RSASHA1; key id = 23550 + example.com. 300 IN RRSIG DNSKEY 7 2 300 ( + 20210208000000 20210105230000 23550 mydnssecgood.org. + Qw9Em3dDok...bNCS7KISw= ) + example.com. 300 IN RRSIG DNSKEY 7 2 300 ( + 20210208000000 20210105230000 29747 mydnssecgood.org. + OuelpIlpY9...XfsKupQgc= ) + ... + +Since the key with the ID 24828 is gone, you can now remove the old DS +record for that key from our parent zone. +Be careful to remove the correct DS record. If you accidentally remove +the new DS record(s) with key ID 23550, it could lead to a problem called +"security lameness," as discussed in +:ref:`troubleshooting_security_lameness`, and may cause users to be unable +to resolve any names in the zone. + +1. After logging in (again, GoDaddy.com in our example) and launching the domain, scroll down to the "DS + Records" section and click Manage. + + .. _remove-ds-1: + + .. figure:: ../dnssec-guide/img/remove-ds-1.png + :alt: Remove DS Record Step #1 + :width: 40.0% + + Remove DS Record Step #1 + +2. A dialog appears, displaying both keys (24828 and 23550). Use the far + right-hand X button to remove key 24828. + + .. _remove-ds-2: + + .. figure:: ../dnssec-guide/img/remove-ds-2.png + :alt: Remove DS Record Step #2 + :width: 80.0% + + Remove DS Record Step #2 + +3. Key 24828 now appears crossed out; click "Save" to complete the + removal. + + .. _remove-ds-3: + + .. figure:: ../dnssec-guide/img/remove-ds-3.png + :alt: Remove DS Record Step #3 + :width: 80.0% + + Remove DS Record Step #3 + +Congratulations, the KSK rollover is complete! As for the actual key +files (ending in ``.key`` and ``.private``), they may be deleted at this +point, but they do not have to be. + +.. [#] + The screenshots were taken from GoDaddy's interface at the time the + original version of this guide was published (2015). It may have + changed since then. + +.. _recipes_nsec3: + +NSEC and NSEC3 +~~~~~~~~~~~~~~ + +.. _recipes_nsec_to_nsec3: + +Migrating from NSEC to NSEC3 +^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +This recipe describes how to transition from using NSEC to NSEC3, as described +in :ref:`advanced_discussions_proof_of_nonexistence`. This recipe +assumes that the zones are already signed, and that ``named`` is configured +according to the steps described in +:ref:`easy_start_guide_for_authoritative_servers`. + +.. warning:: + + If your zone is signed with RSASHA1 (algorithm 5), you cannot migrate + to NSEC3 without also performing an + algorithm rollover + to RSASHA1-NSEC3-SHA1 (algorithm 7), as described in + :ref:`advanced_discussions_DNSKEY_algorithm_rollovers`. This + ensures that older validating resolvers that do not understand + NSEC3 will fall back to treating the zone as unsecured (rather than + "bogus"), as described in Section 2 of :rfc:`5155`. + +To enable NSEC3, update your ``dnssec-policy`` and add the desired NSEC3 +parameters. The example below enables NSEC3 for zones with the ``standard`` +DNSSEC policy, using 0 additional iterations, no opt-out, and a zero-length salt: + +:: + + dnssec-policy "standard" { + nsec3param iterations 0 optout no salt-length 0; + }; + +Then reconfigure the server with ``rndc``. You can tell that it worked if you +see the following debug log messages: + +:: + + Oct 21 13:47:21 received control channel command 'reconfig' + Oct 21 13:47:21 zone example.com/IN (signed): zone_addnsec3chain(1,CREATE,0,-) + +You can also verify that it worked by querying for a name that you know +does not exist, and checking for the presence of the NSEC3 record. +For example: + +:: + + $ dig @192.168.1.13 thereisnowaythisexists.example.com. A +dnssec +multiline + + ... + 5A03TL362CS8VSIH69CVA4MJIKRHFQH3.example.com. 300 IN NSEC3 1 0 0 - ( + TQ9QBEGA6CROHEOC8KIH1A2C06IVQ5ER + NS SOA RRSIG DNSKEY NSEC3PARAM ) + ... + +Our example used four parameters: 1, 0, 0, and -, in +order. 1 represents the algorithm, 0 represents the +opt-out flag, 0 represents the number of additional iterations, and +- denotes no salt is used. To learn more about each of these +parameters, please see :ref:`advanced_discussions_nsec3param`. + +.. _recipes_nsec3_to_nsec: + +Migrating from NSEC3 to NSEC +^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Migrating from NSEC3 back to NSEC is easy; just remove the ``nsec3param`` +configuration option from your ``dnssec-policy`` and reconfigure the name +server. You can tell that it worked if you see these messages in the log: + +:: + + named[14093]: received control channel command 'reconfig' + named[14093]: zone example.com/IN: zone_addnsec3chain(1,REMOVE,0,-) + +You can also query for a name that you know does not exist, +and you should no longer see any traces of NSEC3 records. + +:: + + $ dig @192.168.1.13 reieiergiuhewhiouwe.example.com. A +dnssec +multiline + + ... + example.com. 300 IN NSEC aaa.example.com. NS SOA RRSIG NSEC DNSKEY + ... + ns1.example.com. 300 IN NSEC web.example.com. A RRSIG NSEC + ... + +.. _recipes_nsec3_optout: + +NSEC3 Opt-Out +^^^^^^^^^^^^^ + +This recipe discusses how to enable and disable NSEC3 opt-out, and how to show +the results of each action. As discussed in +:ref:`advanced_discussions_nsec3_optout`, NSEC3 opt-out is a feature +that can help conserve resources on parent zones with many +delegations that have not yet been signed. + +.. warning:: + NSEC3 Opt-Out feature brings benefit only to _extremely_ large zones with lots + of insecure delegations. It's use is counterproductive in all other cases as + it decreases tamper-resistance of the zone and also decreases efficiency of + resolver cache (see :rfc:`8198`). + + In other words, don't enable Opt-Out unless you are serving an equivalent of + ``com.`` zone. + +Because the NSEC3PARAM record does not keep track of whether opt-out is used, +it is hard to check whether changes need to be made to the NSEC3 chain if the flag +is changed. Similar to changing the NSEC3 salt, your best option is to change +the value of ``optout`` together with another NSEC3 parameter, like +``iterations``, and in a following step restore the ``iterations`` value. + +For this recipe we assume the zone ``example.com`` +has the following four entries (for this example, it is not relevant what +record types these entries are): + +- ``ns1.example.com`` + +- ``ftp.example.com`` + +- ``www.example.com`` + +- ``web.example.com`` + +And the zone ``example.com`` has five delegations to five subdomains, only one of +which is signed and has a valid DS RRset: + +- ``aaa.example.com``, not signed + +- ``bbb.example.com``, signed + +- ``ccc.example.com``, not signed + +- ``ddd.example.com``, not signed + +- ``eee.example.com``, not signed + +Before enabling NSEC3 opt-out, the zone ``example.com`` contains ten +NSEC3 records; below is the list with the plain text name before the actual +NSEC3 record: + +- *aaa.example.com*: IFA1I3IE7EKCTPHM6R58URO3Q846I52M.example.com + +- *bbb.example.com*: ROJUF3VJSJO6LQ2LC1DNSJ5GBAUJPVHE.example.com + +- *ccc.example.com*: 0VPUT696LUVDPDS5NIHSHBH9KLV20V5K.example.com + +- *ddd.example.com*: UHPBD5U4HRGB84MLC2NQOVEFNAKJU0CA.example.com + +- *eee.example.com*: NF7I61FA4C2UEKPMEDSOC25FE0UJIMKT.example.com + +- *ftp.example.com*: 8P15KCUAT1RHCSDN46HBQVPI5T532IN1.example.com + +- *ns1.example.com*: GUFVRA2SFIO8RSFP7UO41E8AD1KR41FH.example.com + +- *web.example.com*: CVQ4LA4ALPQIAO2H3N2RB6IR8UHM91E7.example.com + +- *www.example.com*: MIFDNDT3NFF3OD53O7TLA1HRFF95JKUK.example.com + +- *example.com*: ONIB9MGUB9H0RML3CDF5BGRJ59DKJHVK.example.com + +We can enable NSEC3 opt-out with the following configuration, changing +the ``optout`` configuration value from ``no`` to ``yes``: + +:: + + dnssec-policy "standard" { + nsec3param iterations 0 optout yes salt-length 0; + }; + +After NSEC3 opt-out is enabled, the number of NSEC3 records is reduced. +Notice that the unsigned delegations ``aaa``, ``ccc``, ``ddd``, and +``eee`` no longer have corresponding NSEC3 records. + +- *bbb.example.com*: ROJUF3VJSJO6LQ2LC1DNSJ5GBAUJPVHE.example.com + +- *ftp.example.com*: 8P15KCUAT1RHCSDN46HBQVPI5T532IN1.example.com + +- *ns1.example.com*: GUFVRA2SFIO8RSFP7UO41E8AD1KR41FH.example.com + +- *web.example.com*: CVQ4LA4ALPQIAO2H3N2RB6IR8UHM91E7.example.com + +- *www.example.com*: MIFDNDT3NFF3OD53O7TLA1HRFF95JKUK.example.com + +- *example.com*: ONIB9MGUB9H0RML3CDF5BGRJ59DKJHVK.example.com + +To undo NSEC3 opt-out, change the configuration again: + +:: + + dnssec-policy "standard" { + nsec3param iterations 0 optout no salt-length 0; + }; + +.. note:: + + NSEC3 hashes the plain text domain name, and we can compute our own + hashes using the tool ``nsec3hash``. For example, to compute the + hashed name for ``www.example.com`` using the parameters we listed + above, we can execute this command: + + :: + + # nsec3hash - 1 0 www.example.com. + MIFDNDT3NFF3OD53O7TLA1HRFF95JKUK (salt=-, hash=1, iterations=0) + +.. _revert_to_unsigned: + +Reverting to Unsigned +~~~~~~~~~~~~~~~~~~~~~ + +This recipe describes how to revert from a signed zone (DNSSEC) back to +an unsigned (DNS) zone. + +Here is what :iscman:`named.conf` looks like when it is signed: + +.. code-block:: none + :emphasize-lines: 4 + + zone "example.com" IN { + type primary; + file "db/example.com.db"; + dnssec-policy "default"; + inline-signing yes; + }; + +To indicate the reversion to unsigned, change the ``dnssec-policy`` line: + +.. code-block:: none + :emphasize-lines: 4 + + zone "example.com" IN { + type primary; + file "db/example.com.db"; + dnssec-policy "insecure"; + inline-signing yes; + }; + +Then use :option:`rndc reload` to reload the zone. + +The "insecure" policy is a built-in policy (like "default"). It makes sure +the zone is still DNSSEC-maintained, to allow for a graceful transition to +unsigned. It also publishes the CDS and CDNSKEY DELETE records automatically +at the appropriate time. + +If the parent zone allows management of DS records via CDS/CDNSKEY, as described in +:rfc:`8078`, the DS record should be removed from the parent automatically. + +Otherwise, DS records can be removed via the registrar. Below is an example +showing how to remove DS records using the +`GoDaddy <https://www.godaddy.com>`__ web-based interface: + +1. After logging in, click the green "Launch" button next to the domain + name you want to manage. + +.. _unsign-1: + + .. figure:: ../dnssec-guide/img/unsign-1.png + :alt: Revert to Unsigned Step #1 + :width: 60.0% + + Revert to Unsigned Step #1 + +2. Scroll down to the "DS Records" section and click Manage. + +.. _unsign-2: + + .. figure:: ../dnssec-guide/img/unsign-2.png + :alt: Revert to Unsigned Step #2 + :width: 40.0% + + Revert to Unsigned Step #2 + +3. A dialog appears, displaying all current keys. Use the far right-hand + X button to remove each key. + +.. _unsign-3: + + .. figure:: ../dnssec-guide/img/unsign-3.png + :alt: Revert to Unsigned Step #3 + :width: 70.0% + + Revert to Unsigned Step #3 + +4. Click Save. + +.. _unsign-4: + + .. figure:: ../dnssec-guide/img/unsign-4.png + :alt: Revert to Unsigned Step #4 + :width: 70.0% + + Revert to Unsigned Step #4 + +When the DS records have been removed from the parent zone, use +``rndc dnssec -checkds -key <id> withdrawn example.com`` to tell ``named`` that +the DS is removed, and the remaining DNSSEC records will be removed in a timely +manner. Or, if parental agents are configured, the DNSSEC records will be +automatically removed after BIND has seen that the parental agents no longer +serve the DS RRset for this zone. + +After a while, the zone is reverted back to the traditional, insecure DNS +format. This can be verified by checking that all DNSKEY and RRSIG records have been +removed from the zone. + +The ``dnssec-policy`` line can then be removed from :iscman:`named.conf` and +the zone reloaded. The zone will no longer be subject to any DNSSEC +maintenance. diff --git a/doc/dnssec-guide/signing.rst b/doc/dnssec-guide/signing.rst new file mode 100644 index 0000000..9bd5371 --- /dev/null +++ b/doc/dnssec-guide/signing.rst @@ -0,0 +1,1647 @@ +.. Copyright (C) Internet Systems Consortium, Inc. ("ISC") +.. +.. SPDX-License-Identifier: MPL-2.0 +.. +.. This Source Code Form is subject to the terms of the Mozilla Public +.. License, v. 2.0. If a copy of the MPL was not distributed with this +.. file, you can obtain one at https://mozilla.org/MPL/2.0/. +.. +.. See the COPYRIGHT file distributed with this work for additional +.. information regarding copyright ownership. + +.. _dnssec_signing: + +Signing +------- + +.. _easy_start_guide_for_authoritative_servers: + +Easy-Start Guide for Signing Authoritative Zones +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +This section provides the basic information needed to set up a +DNSSEC-enabled authoritative name server. A DNSSEC-enabled (or +"signed") zone contains additional resource records that are used to +verify the authenticity of its zone information. + +To convert a traditional (insecure) DNS zone to a secure one, we need to +create some additional records (DNSKEY, RRSIG, and NSEC or NSEC3), and +upload verifiable information (such as a DS record) to the parent zone to +complete the chain of trust. For more information about DNSSEC resource +records, please see :ref:`what_does_dnssec_add_to_dns`. + +.. note:: + + In this chapter, we assume all configuration files, key files, and + zone files are stored in ``/etc/bind``, and most examples show + commands run as the root user. This may not be ideal, but the point is + not to distract from what is important here: learning how to sign + a zone. There are many best practices for deploying a more secure + BIND installation, with techniques such as jailed process and + restricted user privileges, but those are not covered + in this document. We trust you, a responsible DNS + administrator, to take the necessary precautions to secure your + system. + +For the examples below, we work with the assumption that +there is an existing insecure zone ``example.com`` that we are +converting to a secure zone. + +.. _signing_easy_start_policy_enable: + +Enabling Automated DNSSEC Zone Maintenance and Key Generation +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +To sign a zone, add the following statement to its +``zone`` clause in the BIND 9 configuration file: + +:: + + options { + directory "/etc/bind"; + recursion no; + ... + }; + + zone "example.com" in { + ... + dnssec-policy default; + inline-signing yes; + ... + }; + +The ``dnssec-policy`` statement causes the zone to be signed and turns +on automatic maintenance for the zone. This includes re-signing the zone +as signatures expire and replacing keys on a periodic basis. The value +``default`` selects the default policy, which contains values suitable +for most situations. We cover the creation of a custom policy in +:ref:`signing_custom_policy`, but for the moment we are accepting the +default values. + +Using ``dnssec-policy`` requires dynamic DNS or ``inline-signing`` +to be enabled. + +.. note:: + + Previously, if a zone with a ``dnssec-policy`` did not have dynamic + DNS set up and ``inline-signing`` was not explicity set, BIND 9 used + inline-signing implicitly. But this caused a lot of problems when operators + switched on or off dynamic DNS for their zones. Therefor, you now have to + configure it explicitly. + +When the configuration file is updated, tell ``named`` to +reload the configuration file by running ``rndc reconfig``: + +:: + + # rndc reconfig + +And that's it - BIND signs your zone. + +At this point, before you go away and merrily add ``dnssec-policy`` +statements to all your zones, we should mention that, like a number of +other BIND configuration options, its scope depends on where it is placed. In +the example above, we placed it in a ``zone`` clause, so it applied only +to the zone in question. If we had placed it in a ``view`` clause, it +would have applied to all zones in the view; and if we had placed it in +the ``options`` clause, it would have applied to all zones served by +this instance of BIND. + +.. _signing_verification: + +Verification +^^^^^^^^^^^^ + +The BIND 9 reconfiguration starts the process of signing the zone. +First, it generates a key for the zone and includes it +in the published zone. The log file shows messages such as these: + +:: + + 07-Apr-2020 16:02:55.045 zone example.com/IN (signed): reconfiguring zone keys + 07-Apr-2020 16:02:55.045 reloading configuration succeeded + 07-Apr-2020 16:02:55.046 keymgr: DNSKEY example.com/ECDSAP256SHA256/10376 (CSK) created for policy default + 07-Apr-2020 16:02:55.046 Fetching example.com/ECDSAP256SHA256/10376 (CSK) from key repository. + 07-Apr-2020 16:02:55.046 DNSKEY example.com/ECDSAP256SHA256/10376 (CSK) is now published + 07-Apr-2020 16:02:55.046 DNSKEY example.com/ECDSAP256SHA256/10376 (CSK) is now active + 07-Apr-2020 16:02:55.048 zone example.com/IN (signed): next key event: 07-Apr-2020 18:07:55.045 + +It then starts signing the zone. How long this process takes depends on the +size of the zone, the speed of the server, and how much activity is +taking place. We can check what is happening by using ``rndc``, +entering the command: + +:: + + # rndc signing -list example.com + +While the signing is in progress, the output is something like: + +:: + + Signing with key 10376/ECDSAP256SHA256 + +and when it is finished: + +:: + + Done signing with key 10376/ECDSAP256SHA256 + +When the second message appears, the zone is signed. + +Before moving on to the next step of coordinating with the parent zone, +let's make sure everything looks good using ``delv``. We want to +simulate what a validating resolver will check, by telling +``delv`` to use a specific trust anchor. + +First, we need to make a copy of the key created by BIND. This +is in the directory you set with the ``directory`` statement in +your configuration file's ``options`` clause, and is named something +like ``Kexample.com.+013.10376.key``: + +:: + + # cp /etc/bind/Kexample.com.+013+10376.key /tmp/example.key + +The original key file looks like this (with the actual key shortened for ease of display, +and comments omitted): + +:: + + # cat /etc/bind/Kexample.com.+013+10376.key + + ... + example.com. 3600 IN DNSKEY 257 3 13 6saiq99qDB...dqp+o0dw== + +We want to edit the copy to be in the ``trust-anchors`` format, so that +it looks like this: + +:: + + # cat /tmp/example.key + trust-anchors { + example.com. static-key 257 3 13 "6saiq99qDB...dqp+o0dw=="; + }; + +Now we can run the ``delv`` command and instruct it to use this +trusted-key file to validate the answer it receives from the +authoritative name server 192.168.1.13: + +:: + + $ delv @192.168.1.13 -a /tmp/example.key +root=example.com example.com. SOA +multiline + ; fully validated + example.com. 600 IN SOA ns1.example.com. admin.example.com. ( + 2020040703 ; serial + 1800 ; refresh (30 minutes) + 900 ; retry (15 minutes) + 2419200 ; expire (4 weeks) + 300 ; minimum (5 minutes) + ) + example.com. 600 IN RRSIG SOA 13 2 600 ( + 20200421150255 20200407140255 10376 example.com. + jBsz92zwAcGMNV/yu167aKQZvFyC7BiQe1WEnlogdLTF + oq4yBQumOhO5WX61LjA17l1DuLWcd/ASwlUZWFGCYQ== ) + +.. _signing_easy_start_upload_to_parent_zone: + +Uploading Information to the Parent Zone +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Once everything is complete on our name server, we need to generate some +information to be uploaded to the parent zone to complete the chain of +trust. The format and the upload methods are actually dictated by your +parent zone's administrator, so contact your registrar or parent zone +administrator to find out what the actual format should be and how to +deliver or upload the information to the parent zone. + +What about your zone between the time you signed it and the time your +parent zone accepts the upload? To the rest of the world, your +zone still appears to be insecure, because if a validating +resolver attempts to validate your domain name via +your parent zone, your parent zone will indicate that you are +not yet signed (as far as it knows). The validating resolver will then +give up attempting to validate your domain name, and will fall back to the +insecure DNS. Until you complete this final step with your +parent zone, your zone remains insecure. + +.. note:: + + Before uploading to your parent zone, verify that your newly signed + zone has propagated to all of your name servers (usually via zone + transfers). If some of your name servers still have unsigned zone + data while the parent tells the world it should be signed, validating + resolvers around the world cannot resolve your domain name. + +Here are some examples of what you may upload to your parent zone, with +the DNSKEY/DS data shortened for display. Note that no matter what +format may be required, the end result is the parent zone +publishing DS record(s) based on the information you upload. Again, +contact your parent zone administrator(s) to find out the +correct format for their system. + +1. DS record format: + + :: + + example.com. 3600 IN DS 10376 13 2 B92E22CAE0...33B8312EF0 + +2. DNSKEY format: + + :: + + example.com. 3600 IN DNSKEY 257 3 13 6saiq99qDB...dqp+o0dw== + +The DS record format may be generated from the DNSKEY using the +``dnssec-dsfromkey`` tool, which is covered in +:ref:`parent_ds_record_format`. For more details and examples on how +to work with your parent zone, please see +:ref:`working_with_parent_zone`. + +.. _signing_easy_start_so_what_now: + +So... What Now? +^^^^^^^^^^^^^^^ + +Congratulations! Your zone is signed, your secondary servers have +received the new zone data, and the parent zone has accepted your upload +and published your DS record. Your zone is now officially +DNSSEC-enabled. What happens next? That is basically it - BIND +takes care of everything else. As for updating your zone file, you can +continue to update it the same way as prior to signing your +zone; the normal work flow of editing a zone file and using the ``rndc`` +command to reload the zone still works as usual, and although you are +editing the unsigned version of the zone, BIND generates the signed +version automatically. + +Curious as to what all these commands did to your zone file? Read on to +:ref:`your_zone_before_and_after_dnssec` and find out. If you are +interested in how to roll this out to your existing primary and +secondary name servers, check out :ref:`recipes_inline_signing` in +the :ref:`dnssec_recipes` chapter. + +.. _your_zone_before_and_after_dnssec: + +Your Zone, Before and After DNSSEC +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +When we assigned the default DNSSEC policy to the zone, we provided the +minimal amount of information to convert a traditional DNS +zone into a DNSSEC-enabled zone. This is what the zone looked like +before we started: + +:: + + $ dig @192.168.1.13 example.com. AXFR +multiline +onesoa + + ; <<>> DiG 9.16.0 <<>> @192.168.1.13 example.com AXFR +multiline +onesoa + ; (1 server found) + ;; global options: +cmd + example.com. 600 IN SOA ns1.example.com. admin.example.com. ( + 2020040700 ; serial + 1800 ; refresh (30 minutes) + 900 ; retry (15 minutes) + 2419200 ; expire (4 weeks) + 300 ; minimum (5 minutes) + ) + example.com. 600 IN NS ns1.example.com. + ftp.example.com. 600 IN A 192.168.1.200 + ns1.example.com. 600 IN A 192.168.1.1 + web.example.com. 600 IN CNAME www.example.com. + www.example.com. 600 IN A 192.168.1.100 + +Below shows the test zone ``example.com`` after reloading the +server configuration. Clearly, the zone grew in size, and the +number of records multiplied: + +:: + + # dig @192.168.1.13 example.com. AXFR +multiline +onesoa + + ; <<>> DiG 9.16.0 <<>> @192.168.1.13 example.com AXFR +multiline +onesoa + ; (1 server found) + ;; global options: +cmd + example.com. 600 IN SOA ns1.example.com. admin.example.com. ( + 2020040703 ; serial + 1800 ; refresh (30 minutes) + 900 ; retry (15 minutes) + 2419200 ; expire (4 weeks) + 300 ; minimum (5 minutes) + ) + example.com. 300 IN RRSIG NSEC 13 2 300 ( + 20200413050536 20200407140255 10376 example.com. + drtV1rJbo5OMi65OJtu7Jmg/thgpdTWrzr6O3Pzt12+B + oCxMAv3orWWYjfP2n9w5wj0rx2Mt2ev7MOOG8IOUCA== ) + example.com. 300 IN NSEC ftp.example.com. NS SOA RRSIG NSEC DNSKEY TYPE65534 + example.com. 600 IN RRSIG NS 13 2 600 ( + 20200413130638 20200407140255 10376 example.com. + 2ipmzm1Ei6vfE9OLowPMsxLBCbjrCpWPgWJ0ekwZBbux + MLffZOXn8clt0Ql2U9iCPdyoQryuJCiojHSE2d6nrw== ) + example.com. 600 IN RRSIG SOA 13 2 600 ( + 20200421150255 20200407140255 10376 example.com. + jBsz92zwAcGMNV/yu167aKQZvFyC7BiQe1WEnlogdLTF + oq4yBQumOhO5WX61LjA17l1DuLWcd/ASwlUZWFGCYQ== ) + example.com. 0 IN RRSIG TYPE65534 13 2 0 ( + 20200413050536 20200407140255 10376 example.com. + Xjkom24N6qeCJjg9BMUfuWf+euLeZB169DHvLYZPZNlm + GgM2czUDPio6VpQbUw6JE5DSNjuGjgpgXC5SipC42g== ) + example.com. 3600 IN RRSIG DNSKEY 13 2 3600 ( + 20200421150255 20200407140255 10376 example.com. + maK75+28oUyDtci3V7wjTsuhgkLUZW+Q++q46Lea6bKn + Xj77kXcLNogNdUOr5am/6O6cnPeJKJWsnmTLISm62g== ) + example.com. 0 IN TYPE65534 \# 5 ( 0D28880001 ) + example.com. 3600 IN DNSKEY 257 3 13 ( + 6saiq99qDBb5b4G4cx13cPjFTrIvUs3NW44SvbbHorHb + kXwOzeGAWyPORN+pwEV/LP9+FHAF/JzAJYdqp+o0dw== + ) ; KSK; alg = ECDSAP256SHA256 ; key id = 10376 + example.com. 600 IN NS ns1.example.com. + ftp.example.com. 600 IN RRSIG A 13 3 600 ( + 20200413130638 20200407140255 10376 example.com. + UYo1njeUA49VhKnPSS3JO4G+/Xd2PD4m3Vaacnd191yz + BIoouEBAGPcrEM2BNrgR0op1EWSus9tG86SM1ZHGuQ== ) + ftp.example.com. 300 IN RRSIG NSEC 13 3 300 ( + 20200413130638 20200407140255 10376 example.com. + rPADrAMAPIPSF3S45OSY8kXBTYMS3nrZg4Awj7qRL+/b + sOKy6044MbIbjg+YWL69dBjKoTSeEGSCSt73uIxrYA== ) + ftp.example.com. 300 IN NSEC ns1.example.com. A RRSIG NSEC + ftp.example.com. 600 IN A 192.168.1.200 + ns1.example.com. 600 IN RRSIG A 13 3 600 ( + 20200413130638 20200407140255 10376 example.com. + Yeojg7qrJmxL6uLTnALwKU5byNldZ9Ggj5XjcbpPvujQ + ocG/ovGBg6pdugXC9UxE39bCDl8dua1frjDcRCCZAA== ) + ns1.example.com. 300 IN RRSIG NSEC 13 3 300 ( + 20200413130638 20200407140255 10376 example.com. + vukgQme6k7JwCf/mJOOzHXbE3fKtSro+Kc10T6dHMdsc + oM1/oXioZvgBZ9cKrQhIAUt7r1KUnrUwM6Je36wWFA== ) + ns1.example.com. 300 IN NSEC web.example.com. A RRSIG NSEC + ns1.example.com. 600 IN A 192.168.1.1 + web.example.com. 600 IN RRSIG CNAME 13 3 600 ( + 20200413130638 20200407140255 10376 example.com. + JXi4WYypofD5geUowVqlqJyHzvcRnsvU/ONhTBaUCw5Y + XtifKAXRHWrUL1HIwt37JYPLf5uYu90RfkWLj0GqTQ== ) + web.example.com. 300 IN RRSIG NSEC 13 3 300 ( + 20200413130638 20200407140255 10376 example.com. + XF4Hsd58dalL+s6Qu99bG80PQyMf7ZrHEzDiEflRuykP + DfBRuf34z27vj70LO1lp2ZiX4BB1ahcEK2ae9ASAmA== ) + web.example.com. 300 IN NSEC www.example.com. CNAME RRSIG NSEC + web.example.com. 600 IN CNAME www.example.com. + www.example.com. 600 IN RRSIG A 13 3 600 ( + 20200413050536 20200407140255 10376 example.com. + mACKXrDOF5JMWqncSiQ3pYWA6abyGDJ4wgGCumjLXhPy + 0cMzJmKv2s7G6+tW3TsA6BK3UoMfv30oblY2Mnl4/A== ) + www.example.com. 300 IN RRSIG NSEC 13 3 300 ( + 20200413050536 20200407140255 10376 example.com. + 1YQ22odVt0TeP5gbNJwkvS684ipDmx6sEOsF0eCizhCv + x8osuOATdlPjIEztt+rveaErZ2nsoLor5k1nQAHsbQ== ) + www.example.com. 300 IN NSEC example.com. A RRSIG NSEC + www.example.com. 600 IN A 192.168.1.100 + +But this is a really messy way to tell if the zone is set up properly +with DNSSEC. Fortunately, there are tools to help us with that. Read on +to :ref:`how_to_test_authoritative_server` to learn more. + +.. _how_to_test_authoritative_server: + +How To Test Authoritative Zones +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +So we've activated DNSSEC and uploaded some data to our parent zone. How +do we know our zone is signed correctly? Here are a few ways to check. + +.. _signing_verify_key_data: + +Look for Key Data in Your Zone +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +One way to see if your zone is signed is to check for the +presence of DNSKEY record types. In our example, we created a single +key, and we expect to see it returned when we query for it. + +:: + + $ dig @192.168.1.13 example.com. DNSKEY +multiline + + ; <<>> DiG 9.16.0 <<>> @10.53.0.6 example.com DNSKEY +multiline + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 18637 + ;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1 + ;; WARNING: recursion requested but not available + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags:; udp: 4096 + ; COOKIE: efe186423313fb66010000005e8c997e99864f7d69ed7c11 (good) + ;; QUESTION SECTION: + ;example.com. IN DNSKEY + + ;; ANSWER SECTION: + example.com. 3600 IN DNSKEY 257 3 13 ( + 6saiq99qDBb5b4G4cx13cPjFTrIvUs3NW44SvbbHorHb + kXwOzeGAWyPORN+pwEV/LP9+FHAF/JzAJYdqp+o0dw== + ) ; KSK; alg = ECDSAP256SHA256 ; key id = 10376 + + +.. _signing_verify_signature: + +Look for Signatures in Your Zone +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Another way to see if your zone data is signed is to check for the +presence of a signature. With DNSSEC, every record [#]_ now comes with at +least one corresponding signature, known as an RRSIG. + +:: + + $ dig @192.168.1.13 example.com. SOA +dnssec +multiline + + ; <<>> DiG 9.16.0 <<>> @10.53.0.6 example.com SOA +dnssec +multiline + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 45219 + ;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1 + ;; WARNING: recursion requested but not available + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags: do; udp: 4096 + ; COOKIE: 75adff4f4ce916b2010000005e8c99c0de47eabb7951b2f5 (good) + ;; QUESTION SECTION: + ;example.com. IN SOA + + ;; ANSWER SECTION: + example.com. 600 IN SOA ns1.example.com. admin.example.com. ( + 2020040703 ; serial + 1800 ; refresh (30 minutes) + 900 ; retry (15 minutes) + 2419200 ; expire (4 weeks) + 300 ; minimum (5 minutes) + ) + example.com. 600 IN RRSIG SOA 13 2 600 ( + 20200421150255 20200407140255 10376 example.com. + jBsz92zwAcGMNV/yu167aKQZvFyC7BiQe1WEnlogdLTF + oq4yBQumOhO5WX61LjA17l1DuLWcd/ASwlUZWFGCYQ== ) + +The serial number was automatically incremented from the old, unsigned +version. ``named`` keeps track of the serial number of the signed version of +the zone independently of the unsigned version. If the unsigned zone is +updated with a new serial number that is higher than the one in the +signed copy, then the signed copy is increased to match it; +otherwise, the two are kept separate. + +.. _signing_verify_zone_file: + +Examine the Zone File +^^^^^^^^^^^^^^^^^^^^^ + +Our original zone file ``example.com.db`` remains untouched, and ``named`` has +generated three additional files automatically for us (shown below). The +signed DNS data is stored in ``example.com.db.signed`` and in the +associated journal file. + +:: + + # cd /etc/bind + # ls + example.com.db example.com.db.jbk example.com.db.signed example.com.db.signed.jnl + +A quick description of each of the files: + +- ``.jbk``: a transient file used by ``named`` + +- ``.signed``: the signed version of the zone in raw format + +- ``.signed.jnl``: a journal file for the signed version of the zone + +These files are stored in raw (binary) format for faster loading. To +reveal the human-readable version, use ``named-compilezone`` +as shown below. In the example below, we run the command on the +raw format zone ``example.com.db.signed`` to produce a text version of +the zone ``example.com.text``: + +:: + + # named-compilezone -f raw -F text -o example.com.text example.com example.com.db.signed + zone example.com/IN: loaded serial 2014112008 (DNSSEC signed) + dump zone to example.com.text...done + OK + +.. _signing_verify_check_parent: + +Check the Parent +^^^^^^^^^^^^^^^^ + +Although this is not strictly related to whether the zone is +signed, a critical part of DNSSEC is the trust relationship between the +parent and the child. Just because we, the child, have all the correctly +signed records in our zone does not mean it can be fully validated by a +validating resolver, unless our parent's data agrees with ours. To check +if our upload to the parent was successful, ask the parent name server +for the DS record of our child zone; we should get back the DS record(s) +containing the information we uploaded in +:ref:`signing_easy_start_upload_to_parent_zone`: + +:: + + $ dig example.com. DS + + ; <<>> DiG 9.16.0 <<>> example.com DS + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 16954 + ;; flags: qr rd ra ad; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1 + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags:; udp: 4096 + ; COOKIE: db280d5b52576780010000005e8c9bf5b0d8de103d934e5d (good) + ;; QUESTION SECTION: + ;example.com. IN DS + + ;; ANSWER SECTION: + example.com. 61179 IN DS 10376 13 2 B92E22CAE0B41430EC38D3F7EDF1183C3A94F4D4748569250C15EE33B8312EF0 + +.. [#] + Well, almost every record: NS records and glue records for + delegations do not have RRSIG records. If there are + no delegations, then every record in your zone is + signed and comes with its own RRSIG. + +.. _signing_verify_external_tools: + +External Testing Tools +^^^^^^^^^^^^^^^^^^^^^^ + +We recommend two tools, below: Verisign DNSSEC Debugger and DNSViz. Others can +be found via a simple online search. These excellent online tools are an easy +way to verify that your domain name is fully secured. + +.. _signing_verify_external_tools_dnssec_debugger: + +Verisign DNSSEC Debugger +++++++++++++++++++++++++ + +URL: `<https://dnssec-debugger.verisignlabs.com/>`__ + +This tool shows a nice summary of checks performed on your domain name. +You can expand it to view more details for each of the items checked, to +get a detailed report. + +.. figure:: ../dnssec-guide/img/verisign-dnssec-debugger-example.png + :alt: Verisign DNSSEC Debugger + + Verisign DNSSEC Debugger + +.. _signing_verify_external_tools_dnsviz: + +DNSViz +++++++ + +URL: `<https://dnsviz.net/>`__ + +DNSViz provides a visual analysis of the DNSSEC authentication chain for +a domain name and its resolution path in the DNS namespace. + +.. figure:: ../dnssec-guide/img/dnsviz-example-small.png + :alt: DNSViz + :width: 80.0% + + DNSViz + +.. _signing_easy_start_explained: + +Signing Easy Start Explained +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +.. _enable_automatic_maintenance_explained: + +Enable Automatic DNSSEC Maintenance Explained +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Signing a zone requires a number of separate steps: + +- Generation of the keys to sign the zone. + +- Inclusion of the keys into the zone. + +- Signing of the records in the file (including the generation of the + NSEC or NSEC3 records). + +Maintaining a signed zone comprises a set of ongoing tasks: + +- Re-signing the zone as signatures approach expiration. + +- Generation of new keys as the time approaches for a key roll. + +- Inclusion of new keys into the zone when the rollover starts. + +- Transition from signing the zone with the old set of keys to signing + the zone with the new set of keys. + +- Waiting the appropriate interval before removing the old keys from + the zone. + +- Deleting the old keys. + +That is quite complex, and it is all handled in BIND 9 with the single +``dnssec-policy default`` statement. We will see later on (in the +:ref:`signing_custom_policy` section) how these actions can be tuned, by +setting up our own DNSSEC policy with customized parameters. However, in many +cases the defaults are adequate. + +At the time of this writing (mid-2020), ``dnssec-policy`` is still a +relatively new feature in BIND. Although it is the preferred +way to run DNSSEC in a zone, it is not yet able to automatically implement +all the features that are available +with a more "hands-on" approach to signing and key maintenance. For this +reason, we cover alternative signing techniques in +:ref:`signing_alternative_ways`. + +.. _working_with_parent_zone: + +Working With the Parent Zone +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +As mentioned in :ref:`signing_easy_start_upload_to_parent_zone`, +the format of the information uploaded to your parent zone is dictated +by your parent zone administrator. The two main formats are: + +1. DS record format + +2. DNSKEY format + +Check with your parent zone to see which format they require. + +But how can you get each of the formats from your existing data? + +When ``named`` turned on automatic +DNSSEC maintenance, essentially the first thing it did was to create +the DNSSEC keys and put them in the directory you specified in the +configuration file. If you look in that directory, you will see three +files with names like ``Kexample.com.+013+10376.key``, +``Kexample.com.+013+10376.private``, and +``Kexample.com.+013+10376.state``. The one we are interested in is the +one with the ``.key`` suffix, which contains the zone's public key. (The +other files contain the zone's private key and the DNSSEC state +associated with the key.) This public key is used to generate the information we +need to pass to the parent. + +.. _parent_ds_record_format: + +DS Record Format +^^^^^^^^^^^^^^^^ + +Below is an example of a DS record format generated from the KSK we +created earlier (``Kexample.com.+013+10376.key``): + +:: + + # cd /etc/bind + dnssec-dsfromkey Kexample.com.+013+10376.key + example.com. IN DS 10376 13 2 B92E22CAE0B41430EC38D3F7EDF1183C3A94F4D4748569250C15EE33B8312EF0 + +Some registrars ask their customers to manually specify the types of algorithm +and digest used. In this example, 13 represents the algorithm used, and +2 represents the digest type (SHA-256). The key tag or key ID is 10376. + +.. _parent_dnskey_format: + +DNSKEY Format +^^^^^^^^^^^^^ + +Below is an example of the same key ID (10376) using DNSKEY format +(with the actual key shortened for ease of display): + +:: + + example.com. 3600 IN DNSKEY 257 3 13 (6saiq99qDB...dqp+o0dw==) ; key id = 10376 + +The key itself is easy to find (it's difficult to miss that long +base64 string) in the file. + +:: + + # cd /etc/bind + # cat Kexample.com.+013+10376.key + ; This is a key-signing key, keyid 10376, for example.com. + ; Created: 20200407150255 (Tue Apr 7 16:02:55 2020) + ; Publish: 20200407150255 (Tue Apr 7 16:02:55 2020) + ; Activate: 20200407150255 (Tue Apr 7 16:02:55 2020) + example.com. 3600 IN DNSKEY 257 3 13 6saiq99qDB...dqp+o0dw== + +.. _signing_custom_policy: + +Creating a Custom DNSSEC Policy +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The remainder of this section describes the contents of a custom DNSSEC +policy. :ref:`dnssec_advanced_discussions` describes the concepts +involved here and the pros and cons of choosing particular values. If +you are not already familiar with DNSSEC, it may be worth reading that chapter +first. + +Setting up your own DNSSEC policy means that you must include a +``dnssec-policy`` clause in the zone file. This sets values for the +various parameters that affect the signing of zones and the rolling of +keys. The following is an example of such a clause: + +:: + + dnssec-policy standard { + dnskey-ttl 600; + keys { + ksk lifetime 365d algorithm ecdsap256sha256; + zsk lifetime 60d algorithm ecdsap256sha256; + }; + max-zone-ttl 600; + parent-ds-ttl 600; + parent-propagation-delay 2h; + publish-safety 7d; + retire-safety 7d; + signatures-refresh 5d; + signatures-validity 15d; + signatures-validity-dnskey 15d; + zone-propagation-delay 2h; + }; + +The policy has multiple parts: + +- The name must be specified. As each zone can use a different policy, + ``named`` needs to be able to distinguish between policies. This is + done by giving each policy a name, such as ``standard`` in the above + example. + +- The ``keys`` clause lists all keys that should be in the zone, along + with their associated parameters. In this example, we are using the + conventional KSK/ZSK split, with the KSK changed every year and the + ZSK changed every two months (the ``default`` DNSSEC policy sets a + CSK that is never changed). Keys are created using the + ECDSAPS256SHA256 algorithm; each KSK/ZSK pair must have the same + algorithm. A CSK combines the functionality of a ZSK and a KSK. + +- The parameters ending in ``-ttl`` are, as expected, the TTLs of the + associated records. Remember that during a key rollover, + we have to wait for records to expire from caches? The values + here tell BIND 9 the maximum amount of time it has to wait for this to + happen. Values can be set for the DNSKEY records in your zone, the + non-DNSKEY records in your zone, and the DS records in the parent + zone. + +- Another set of time-related parameters are those ending in + ``-propagation-delay``. These tell BIND how long it takes for a + change in zone contents to become available on all secondary servers. + (This may be non-negligible: for example, if a large zone is + transferred over a slow link.) + +- The policy also sets values for the various signature parameters: how + long the signatures on the DNSKEY and non-DNSKEY records are valid, + and how often BIND should re-sign the zone. + +- The parameters ending in ``-safety`` are there to give + you a bit of leeway in case a key roll doesn't go to plan. When + introduced into the zone, the ``publish-safety`` time is the amount + of additional time, over and above that calculated from the other + parameters, during which the new key is in the zone but before BIND starts + to sign records with it. Similarly, the ``retire-safety`` is the + amount of additional time, over and above that calculated from the + other parameters, during which the old key is retained in the zone before + being removed. + +- Finally, the ``purge-keys`` option allows you to clean up key files + automatically after a period of time. If a key has been removed from the + zone, this option will determine how long its key files will be retained + on disk. + +(You do not have to specify all the items listed above in your policy +definition. Any that are not set simply take the default value.) + +Usually, the exact timing of a key roll, or how long a signature remains +valid, is not critical. For this reason, err on the side of caution when +setting values for the parameters. It is better to have an operation +like a key roll take a few days longer than absolutely required, than it +is to have a quick key roll but have users get validation failures +during the process. + +Having defined a new policy called "standard", we now need to tell +``named`` to use it. We do this by adding a ``dnssec-policy standard;`` +statement to the configuration file. Like many other configuration +statements, it can be placed in the ``options`` statement (thus applying +to all zones on the server), a ``view`` statement (applying to all zones +in the view), or a ``zone`` statement (applying only to that zone). In +this example, we'll add it to the ``zone`` statement: + +:: + + zone "example.net" in { + ... + dnssec-policy standard; + inline-signing yes; + ... + }; + +Finally, tell ``named`` to use the new policy: + +:: + + # rndc reconfig + +... and that's it. ``named`` now applies the "standard" policy to +your zone. + +.. _signing_maintenance_tasks: + +Maintenance Tasks +~~~~~~~~~~~~~~~~~ + +Zone data is signed and the parent zone has published your DS records: +at this point your zone is officially secure. When other +validating resolvers look up information in your zone, they are able to +follow the 12-step process as described in +:ref:`how_does_dnssec_change_dns_lookup_revisited` and verify the +authenticity and integrity of the answers. + +There is not that much left for you, as the DNS administrator, to do on +an ongoing basis. Whenever you update your zone, BIND automatically +re-signs your zone with new RRSIG and NSEC/NSEC3 records, and even +increments the serial number for you. If you choose to split your keys +into a KSK and ZSK, the rolling of the ZSK is completely automatic. +Rolling of a KSK or CSK may require some manual intervention, though, +so let's examine two more DNSSEC-related resource records, CDS and CDNSKEY. + +.. _cds_cdnskey: + +The CDS and CDNSKEY Resource Records +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Passing the DS record to the organization running the parent zone has +always been recognized as a bottleneck in the key rollover process. To +automate the process, the CDS and CDNSKEY resource records were +introduced. + +The CDS and CDNSKEY records are identical to the DS and DNSKEY records, +except in the type code and the name. When such a record appears in the +child zone, it is a signal to the parent that it should update the DS it +has for that zone. In essence, when the parent notices +the presence of the CDS and/or CDNSKEY record(s) in the +child zone, it checks these records to verify that they are +signed by a valid key for the zone. If the record(s) successfully +validate, the parent zone's DS RRset for the child zone is changed to +correspond to the CDS (or CDNSKEY) records. (For more +information on how the signaling works and the issues surrounding it, +please refer to :rfc:`7344` and :rfc:`8078`.) + +.. _working_with_the_parent_2: + +Working with the Parent Zone (2) +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Once the zone is signed, the only required manual tasks are +to monitor KSK or CSK key rolls and pass the new DS record to the +parent zone. However, if the parent can process CDS or CDNSKEY records, +you may not even have to do that [#]_. + +When the time approaches for the roll of a KSK or CSK, BIND adds a +CDS and a CDNSKEY record for the key in question to the apex of the +zone. If your parent zone supports polling for CDS/CDNSKEY records, they +are uploaded and the DS record published in the parent - at least ideally. + +If BIND is configured with ``parental-agents``, it will check for the DS +presence. Let's look at the following configuration excerpt: + +:: + + parental-agents "net" { + 10.53.0.11; 10.53.0.12; + }; + + zone "example.net" in { + ... + dnssec-policy standard; + inline-signing yes; + parental-agents { "net"; }; + ... + }; + +BIND will check for the presence of the DS record in the parent zone by querying +its parental agents (defined in :rfc:`7344` to be the entities that the child +zone has a relationship with to change its delegation information). In the +example above, The zone `example.net` is configured with two parental agents, +at the addresses 10.53.0.11 and 10.53.0.12. These addresses are used as an +example only. Both addresses will have to respond with a DS RRset that +includes the DS record identifying the key that is being rolled. If one or +both don't have the DS included yet the rollover is paused, and the check for +DS presence is retried after an hour. The same applies for DS withdrawal. + +Alternatively, you can use the ``rndc`` tool to tell ``named`` that the DS +record has been published or withdrawn. For example: + +:: + + # rndc dnssec -checkds published example.net + +If your parent zone doesn't support CDS/CDNSKEY, you will have to supply +the DNSKEY or DS record to the parent zone manually when a new KSK appears in +your zone, presumably using the same mechanism you used to upload the +records for the first time. Again, you need to use the ``rndc`` tool +to tell ``named`` that the DS record has been published. + +.. [#] + For security reasons, a parent zone that supports CDS/CDNSKEY may require + the DS record to be manually uploaded when we first sign the zone. + Until our zone is signed, the parent cannot be sure that a CDS or CDNSKEY + record it finds by querying our zone really comes from our zone; thus, it + needs to use some other form of secure transfer to obtain the information. + +.. _signing_alternative_ways: + +Alternate Ways of Signing a Zone +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Although use of the automatic ``dnssec-policy`` is the preferred way to sign zones in +BIND, there are occasions where a more manual approach may be +needed, such as when external hardware is used to +generate and sign the zone. ``dnssec-policy`` does not currently support +the use of external hardware, so if your security policy requires it, you +need to use one of the methods described here. + +The idea of DNSSEC was first discussed in the 1990s and has been +extensively developed over the intervening years. BIND has tracked the +development of this technology, often being the first name server +implementation to introduce new features. However, for compatibility reasons, BIND +retained older ways of doing things even when new ways were added. This +particularly applies to signing and maintaining zones, where different +levels of automation are available. + +The following is a list of the available methods of signing in BIND, in the +order that they were introduced - and in order of decreasing +complexity. + +Manual + "Manual" signing was the first method to be introduced into BIND and + its name describes it perfectly: the user needs to do everything. In the + more-automated methods, you load an unsigned zone file into + ``named``, which takes care of signing it. With manual signing, you + have to provide a signed zone for ``named`` to serve. + + In practice, this means creating an unsigned zone file as usual, then + using the BIND-provided tools ``dnssec-keygen`` to create the keys + and ``dnssec-signzone`` to sign the zone. The signed zone is stored + in another file and is the one you tell BIND to load. To + update the zone (for example, to add a resource record), you update the + unsigned zone, re-sign it, and tell ``named`` to load the updated + signed copy. The same goes for refreshing signatures or rolling keys; + the user is responsible for providing the signed zone served by + ``named``. (In the case of rolling keys, you are also responsible for + ensuring that the keys are added and removed at the correct times.) + + Why would you want to sign your zone this way? You probably + wouldn't in the normal course of events, but as there may be + circumstances in which it is required, the scripts have been left in + the BIND distribution. + +Semi-Automatic + The first step in DNSSEC automation came with BIND 9.7, when the + ``auto-dnssec`` option was added. This causes ``named`` to + periodically search the directory holding the key files (see + :ref:`generate_keys` for a description) and to + use the information in them to both add and remove keys and sign the + zone. + + Use of ``auto-dnssec`` alone requires that the zone be dynamic, + something not suitable for a number of situations, so BIND 9.9 added the + ``inline-signing`` option. With this, ``named`` essentially keeps the + signed and unsigned copies of the zone separate. The signed zone is + created from the unsigned one using the key information; when the + unsigned zone is updated and the zone reloaded, ``named`` detects the + changes and updates the signed copy of the zone. + + This mode of signing has been termed "semi-automatic" in this + document because keys still have to be manually created (and deleted + when appropriate). Although not an onerous task, it is still + additional work. + + Why would anyone want to use this + method when fully automated ones are available? At the time of + this writing (mid-2020), the fully automatic methods cannot handle all scenarios, + particularly that of having a single key shared among multiple + zones. They also do not handle keys stored in Hardware Security + Modules (HSMs), which are briefly covered in + :ref:`hardware_security_modules`. + +Fully Automatic with ``dnssec-keymgr`` + The next step in the automation of DNSSEC operations came with BIND + 9.11, which introduced the ``dnssec-keymgr`` utility. This is a + separate program and is expected to be run on a regular basis + (probably via ``cron``). It reads a DNSSEC policy from its + configuration file and reads timing information from the DNSSEC key + files. With this information it creates new key files with timing + information in them consistent with the policy. ``named`` is run as + usual, picking up the timing information in the key files to + determine when to add and remove keys, and when to sign with them. + + In BIND 9.17.0 and later, this method of handling DNSSEC + policies has been replaced by the ``dnssec-policy`` statement in the + configuration file. + +Fully Automatic with ``dnssec-policy`` + Introduced a BIND 9.16, ``dnssec-policy`` replaces ``dnssec-keymgr`` from BIND + 9.17 onwards and avoids the need to run a separate program. It also + handles the creation of keys if a zone is added (``dnssec-keymgr`` + requires an initial key) and deletes old key files as they are + removed from the zone. This is the method described in + :ref:`easy_start_guide_for_authoritative_servers`. + +We now look at some of these methods in more detail. We cover +semi-automatic signing first, as that contains a lot of useful +information about keys and key timings. We then describe what +``dnssec-keymgr`` adds to semi-automatic signing. After that, we +touch on fully automatic signing with ``dnssec-policy``. Since this has +already been described in +:ref:`easy_start_guide_for_authoritative_servers`, we will just +mention a few additional points. Finally, we briefly describe manual signing. + +.. _semi_automatic_signing: + +Semi-Automatic Signing +^^^^^^^^^^^^^^^^^^^^^^ + +As noted above, the term semi-automatic signing has been used in this +document to indicate the mode of signing enabled by the ``auto-dnssec`` +and ``inline-signing`` keywords. ``named`` signs the zone without any +manual intervention, based purely on the timing information in the +DNSSEC key files. The files, however, must be created manually. + +By appropriately setting the key parameters and the timing information +in the key files, you can implement any DNSSEC policy you want for your +zones. But why manipulate the key information yourself rather than rely +on ``dnssec-keymgr`` or ``dnssec-policy`` to do it for you? The answer +is that semi-automatic signing allows you to do things that, at the time of this writing +(mid-2020), are currently not possible with one of the key managers: for +example, the ability to use an HSM to store keys, or the ability to use +the same key for multiple zones. + +To convert a traditional +(insecure) DNS zone to a secure one, we need to create various +additional records (DNSKEY, RRSIG, NSEC/NSEC3) and, as with +fully automatic signing, to upload verifiable information (such as a DS +record) to the parent zone to complete the chain of trust. + +.. note:: + + Again, we assume all configuration files, key + files, and zone files are stored in ``/etc/bind``, and most examples + show commands run + as the root user. This may not be ideal, but the point is not + to distract from what is important here: learning how to sign + a zone. There are many best practices for deploying a more secure + BIND installation, with techniques such as jailed process and + restricted user privileges, but those are not covered + in this document. We trust you, a responsible DNS + administrator, to take the necessary precautions to secure your + system. + + For our examples below, we work with the assumption that + there is an existing insecure zone ``example.com`` that we are + converting to a secure version. The secure version uses both a KSK + and a ZSK. + +.. _generate_keys: + +Generate Keys ++++++++++++++ + +Everything in DNSSEC centers around keys, so we begin by +generating our own keys. + +.. code-block:: console + + # cd /etc/bind/keys + # dnssec-keygen -a ECDSAP256SHA256 example.com + Generating key pair...........................+++++ ......................+++++ + Kexample.com.+013+34371 + # dnssec-keygen -a ECDSAP256SHA256 -f KSK example.com + Generating key pair........................+++ ..................................+++ + Kexample.com.+013+00472 + +This command generates four key files in ``/etc/bind/keys``: + +- Kexample.com.+013+34371.key + +- Kexample.com.+013+34371.private + +- Kexample.com.+013+00472.key + +- Kexample.com.+013+00472.private + +The two files ending in ``.key`` are the public keys. These contain the +DNSKEY resource records that appear in the zone. The two files +ending in ``.private`` are the private keys, and contain the information +that ``named`` actually uses to sign the zone. + +Of the two pairs, one is the zone-signing key (ZSK), and one is the +key-signing key (KSK). We can tell which is which by looking at the file +contents (the actual keys are shortened here for ease of display): + +.. code-block:: console + + # cat Kexample.com.+013+34371.key + ; This is a zone-signing key, keyid 34371, for example.com. + ; Created: 20200616104249 (Tue Jun 16 11:42:49 2020) + ; Publish: 20200616104249 (Tue Jun 16 11:42:49 2020) + ; Activate: 20200616104249 (Tue Jun 16 11:42:49 2020) + example.com. IN DNSKEY 256 3 13 AwEAAfel66...LqkA7cvn8= + # cat Kexample.com.+013+00472.key + ; This is a key-signing key, keyid 472, for example.com. + ; Created: 20200616104254 (Tue Jun 16 11:42:54 2020) + ; Publish: 20200616104254 (Tue Jun 16 11:42:54 2020) + ; Activate: 20200616104254 (Tue Jun 16 11:42:54 2020) + example.com. IN DNSKEY 257 3 13 AwEAAbCR6U...l8xPjokVU= + +The first line of each file tells us what type of key it is. Also, by +looking at the actual DNSKEY record, we can tell them apart: 256 is +ZSK, and 257 is KSK. + +The name of the file also tells us something +about the contents. See chapter :ref:`zone_keys` for more details. + +Make sure that these files are readable by ``named`` and that the +``.private`` files are not readable by anyone else. + +Alternativelly, the ``dnssec-keyfromlabel`` program is used to get a key +pair from a crypto hardware device and build the key files. Its usage is +similar to ``dnssec-keygen``. + +Setting Key Timing Information +++++++++++++++++++++++++++++++ + +You may remember that in the above description of this method, we said +that time information related to rolling keys is stored in the key +files. This is placed there by ``dnssec-keygen`` when the file is +created, and it can be modified using ``dnssec-settime``. By default, +only a limited amount of timing information is included in the file, as +illustrated in the examples in the previous section. + +All the dates are the same, and are the date and time that +``dnssec-keygen`` created the key. We can use ``dnssec-settime`` to +modify the dates [#]_. For example, to publish this key in +the zone on 1 July 2020, use it to sign records for a year starting on +15 July 2020, and remove it from the zone at the end of July 2021, we +can use the following command: + +.. code-block:: console + + # dnssec-settime -P 20200701 -A 20200715 -I 20210715 -D 20210731 Kexample.com.+013+34371.key + ./Kexample.com.+013+34371.key + ./Kexample.com.+013+34371.private + +which would set the contents of the key file to: + +.. code-block:: none + + ; This is a zone-signing key, keyid 34371, for example.com. + ; Created: 20200616104249 (Tue Jun 16 11:42:49 2020) + ; Publish: 20200701000000 (Wed Jul 1 01:00:00 2020) + ; Activate: 20200715000000 (Wed Jul 15 01:00:00 2020) + ; Inactive: 20210715000000 (Thu Jul 15 01:00:00 2021) + ; Delete: 20210731000000 (Sat Jul 31 01:00:00 2021) + example.com. IN DNSKEY 256 3 13 AwEAAfel66...LqkA7cvn8= + +(The actual key is truncated here to improve readability.) + +Below is a complete list of each of the metadata fields, and how each +one affects the signing of your zone: + +1. *Created*: This records the date on which the key was created. It is + not used in calculations; it is useful simply for documentation + purposes. + +2. *Publish*: This sets the date on which a key is to be published to the + zone. After that date, the key is included in the zone but is + not used to sign it. This allows validating resolvers to get a + copy of the new key in their cache before there are any resource + records signed with it. By default, if not specified at creation + time, this is set to the current time, meaning the key is + published as soon as ``named`` picks it up. + +3. *Activate*: This sets the date on which the key is to be activated. After + that date, resource records are signed with the key. By default, + if not specified during creation time, this is set to the current + time, meaning the key is used to sign data as soon as ``named`` + picks it up. + +4. *Revoke:* This sets the date on which the key is to be revoked. After that + date, the key is flagged as revoked, although it is still included in the + zone and used to sign it. This is used to notify validating + resolvers that this key is about to be removed or retired from the + zone. (This state is not used in normal day-to-day operations. See + :rfc:`5011` to understand the circumstances where it may be used.) + +5. *Inactive*: This sets the date on which the key is to become inactive. + After that date, the key is still included in the zone, but it + is no longer used to sign it. This sets the "expiration" or "retire" + date for a key. + +6. *Delete*: This sets the date on which the key is to be deleted. After that + date, the key is no longer included in the zone, but it + continues to exist on the file system or key repository. + +This can be summarized as follows: + +.. table:: Key Metadata Comparison + + +----------+------------------+------------------+------------------+ + | Metadata | Included in Zone | Used to Sign | Purpose | + | | File? | Data? | | + +==========+==================+==================+==================+ + | Created | No | No | Recording of | + | | | | key creation | + +----------+------------------+------------------+------------------+ + | Publish | Yes | No | Introduction of | + | | | | a key soon to be | + | | | | active | + +----------+------------------+------------------+------------------+ + | Activate | Yes | Yes | Activation date | + | | | | for new key | + +----------+------------------+------------------+------------------+ + | Revoke | Yes | Yes | Notification of | + | | | | a key soon to be | + | | | | retired | + +----------+------------------+------------------+------------------+ + | Inactive | Yes | No | Inactivation or | + | | | | retirement of a | + | | | | key | + +----------+------------------+------------------+------------------+ + | Delete | No | No | Deletion or | + | | | | removal of a key | + | | | | from a zone | + +----------+------------------+------------------+------------------+ + +The publication date is the date the key is introduced into the zone. +Sometime later it is activated and is used to sign resource records. +After a specified period, BIND stops using it to sign records, and at some +other specified later time it is removed from the zone. + +Finally, we should note that the ``dnssec-keygen`` command supports the +same set of switches so we could have set the dates +when we created the key. + +.. _semi_automatic_signing_reconfigure_bind: + +Reconfiguring BIND +++++++++++++++++++ + +Having created the keys with the appropriate timing information, the +next step is to turn on DNSSEC signing. Below is a very simple +``named.conf``; in our example environment, this file is +``/etc/bind/named.conf``. + +:: + + options { + directory "/etc/bind"; + recursion no; + minimal-responses yes; + }; + + zone "example.com" IN { + type primary; + file "example.com.db"; + auto-dnssec maintain; + inline-signing yes; + }; + +Once the configuration file is updated, tell ``named`` to +reload: + +:: + + # rndc reload + server reload successful + +.. _semi_automated_signing_verification: + +Verifying That the Zone Is Signed Correctly ++++++++++++++++++++++++++++++++++++++++++++ + +You should now check that the zone is signed. Follow the steps in +:ref:`signing_verification`. + +.. _semi_automatic_signing_upload_ds: + +Uploading the DS Record to the Parent ++++++++++++++++++++++++++++++++++++++ + +As described in :ref:`signing_easy_start_upload_to_parent_zone`, we +must now upload the new information to the parent zone. The format of the +information and how to generate it is described in +:ref:`working_with_parent_zone`, although it is important to remember that you must +use the contents of the KSK file that you generated above as part of the +process. + +When the DS record is published in the parent zone, your zone is fully +signed. + +Checking That Your Zone Can Be Validated +++++++++++++++++++++++++++++++++++++++++ + +Finally, follow the steps in :ref:`how_to_test_authoritative_server` +to confirm that a query recognizes the zone as properly signed and +vouched for by the parent zone. + +So... What Now? ++++++++++++++++ + +Once the zone is signed, it must be monitored as described +in :ref:`signing_maintenance_tasks`. However, +as the time approaches for a key roll, you must create the new key. Of +course, it is possible to create keys for the next fifty +years all at once and set the key times appropriately. Whether the +increased risk in having the private key files for future keys available +on disk offsets the overhead of having to remember to create a new key +before a rollover depends on your organization's security policy. + +.. _advanced_discussions_automatic_dnssec-keymgr: + +Fully Automatic Signing With ``dnssec-keymgr`` +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +``dnssec-keymgr`` is a program supplied with BIND (versions 9.11 to +9.16) to help with key rollovers. When run, it compares the timing +information for existing keys with the defined policy, and adjusts it if +necessary. It also creates additional keys as required. + +``dnssec-keymgr`` is completely separate from ``named``. As we will see, +the policy states a coverage period; ``dnssec-keymgr`` generates +enough key files to handle all rollovers in that period. However, it is +a good idea to schedule it to run on a regular basis; that way there is +no chance of forgetting to run it when the coverage period ends. + +BIND should be set up exactly the same way as described in +:ref:`semi_automatic_signing`, i.e., +with ``auto-dnssec`` set to ``maintain`` and ``inline-signing`` set to +``true``. Then a policy file must be created. The following is an +example of such a file: + +:: + + # cat policy.conf + policy standard { + coverage 1y; + algorithm RSASHA256; + directory "/etc/bind"; + keyttl 2h; + + key-size ksk 4096; + roll-period ksk 1y; + pre-publish ksk 30d; + post-publish ksk 30d; + + key-size zsk 2048; + roll-period zsk 90d; + pre-publish zsk 30d; + post-publish zsk 30d; + }; + + zone example.com { + policy standard; + }; + + zone example.net { + policy standard; + keyttl 300; + }; + +As can be seen, the syntax is similar to that of the ``named`` +configuration file. + +In the example above, we define a DNSSEC policy called "standard". Keys +are created using the RSASHA256 algorithm, assigned a TTL of two hours, +and placed in the directory ``/etc/bind``. KSKs have a key size of +4096 bits and are expected to roll once a year; the new key is added to the +zone 30 days before it becomes active, and is retained in the zone for +30 days after it is rolled. ZSKs have a key size of 2048 bits and roll +every 90 days; like the KSKs, the are added to the zone 30 days before +they are used for signing, and retained for 30 days after ``named`` +ceases signing with them. + +The policy is applied to two zones, ``example.com`` and ``example.net``. +The policy is applied unaltered to the former, but for the latter the +setting for the DNSKEY TTL has been overridden and set to 300 seconds. + +To apply the policy, we need to run ``dnssec-keymgr``. Since this does +not read the ``named`` configuration file, it relies on the presence of +at least one key file for a zone to tell it that the zone is +DNSSEC-enabled. If a key file does not already exist, we first need to create +one for each zone. We can do that either by running +``dnssec-keygen`` to create a key file for each zone [#]_, or by +specifying the zones in question on the command line. Here, we do the +latter: + +:: + + # dnssec-keymgr -c policy.conf example.com example.net + # /usr/local/sbin/dnssec-keygen -q -K /etc/bind -L 7200 -a RSASHA256 -b 2048 example.net + # /usr/local/sbin/dnssec-keygen -q -K /etc/bind -L 7200 -fk -a RSASHA256 -b 4096 example.net + # /usr/local/sbin/dnssec-settime -K /etc/bind -I 20200915110318 -D 20201015110318 Kexample.net.+008+31339 + # /usr/local/sbin/dnssec-keygen -q -K /etc/bind -S Kexample.net.+008+31339 -L 7200 -i 2592000 + # /usr/local/sbin/dnssec-settime -K /etc/bind -I 20201214110318 -D 20210113110318 Kexample.net.+008+14526 + # /usr/local/sbin/dnssec-keygen -q -K /etc/bind -S Kexample.net.+008+14526 -L 7200 -i 2592000 + # /usr/local/sbin/dnssec-settime -K /etc/bind -I 20210314110318 -D 20210413110318 Kexample.net.+008+46069 + # /usr/local/sbin/dnssec-keygen -q -K /etc/bind -S Kexample.net.+008+46069 -L 7200 -i 2592000 + # /usr/local/sbin/dnssec-settime -K /etc/bind -I 20210612110318 -D 20210712110318 Kexample.net.+008+13018 + # /usr/local/sbin/dnssec-keygen -q -K /etc/bind -S Kexample.net.+008+13018 -L 7200 -i 2592000 + # /usr/local/sbin/dnssec-settime -K /etc/bind -I 20210617110318 -D 20210717110318 Kexample.net.+008+55237 + # /usr/local/sbin/dnssec-keygen -q -K /etc/bind -S Kexample.net.+008+55237 -L 7200 -i 2592000 + # /usr/local/sbin/dnssec-keygen -q -K /etc/bind -L 7200 -a RSASHA256 -b 2048 example.com + # /usr/local/sbin/dnssec-keygen -q -K /etc/bind -L 7200 -fk -a RSASHA256 -b 4096 example.com + # /usr/local/sbin/dnssec-settime -K /etc/bind -P 20200617110318 -A 20200617110318 -I 20200915110318 -D 20201015110318 Kexample.com.+008+31168 + # /usr/local/sbin/dnssec-keygen -q -K /etc/bind -S Kexample.com.+008+31168 -L 7200 -i 2592000 + # /usr/local/sbin/dnssec-settime -K /etc/bind -I 20201214110318 -D 20210113110318 Kexample.com.+008+24199 + # /usr/local/sbin/dnssec-keygen -q -K /etc/bind -S Kexample.com.+008+24199 -L 7200 -i 2592000 + # /usr/local/sbin/dnssec-settime -K /etc/bind -I 20210314110318 -D 20210413110318 Kexample.com.+008+08728 + # /usr/local/sbin/dnssec-keygen -q -K /etc/bind -S Kexample.com.+008+08728 -L 7200 -i 2592000 + # /usr/local/sbin/dnssec-settime -K /etc/bind -I 20210612110318 -D 20210712110318 Kexample.com.+008+12874 + # /usr/local/sbin/dnssec-keygen -q -K /etc/bind -S Kexample.com.+008+12874 -L 7200 -i 2592000 + # /usr/local/sbin/dnssec-settime -K /etc/bind -P 20200617110318 -A 20200617110318 Kexample.com.+008+26186 + +This creates enough key files to last for the coverage period, set in +the policy file to be one year. The script should be run on a regular +basis (probably via ``cron``) to keep the reserve of key files topped +up. With the shortest roll period set to 90 days, every 30 days is +more than adequate. + +At any time, you can check what key changes are coming up and whether +the keys and timings are correct by using ``dnssec-coverage``. For +example, to check coverage for the next 60 days: + +:: + + # dnssec-coverage -d 2h -m 1d -l 60d -K /etc/bind/keys + PHASE 1--Loading keys to check for internal timing problems + PHASE 2--Scanning future key events for coverage failures + Checking scheduled KSK events for zone example.net, algorithm RSASHA256... + Wed Jun 17 11:03:18 UTC 2020: + Publish: example.net/RSASHA256/55237 (KSK) + Activate: example.net/RSASHA256/55237 (KSK) + + Ignoring events after Sun Aug 16 11:47:24 UTC 2020 + + No errors found + + Checking scheduled ZSK events for zone example.net, algorithm RSASHA256... + Wed Jun 17 11:03:18 UTC 2020: + Publish: example.net/RSASHA256/31339 (ZSK) + Activate: example.net/RSASHA256/31339 (ZSK) + Sun Aug 16 11:03:18 UTC 2020: + Publish: example.net/RSASHA256/14526 (ZSK) + + Ignoring events after Sun Aug 16 11:47:24 UTC 2020 + + No errors found + + Checking scheduled KSK events for zone example.com, algorithm RSASHA256... + Wed Jun 17 11:03:18 UTC 2020: + Publish: example.com/RSASHA256/26186 (KSK) + Activate: example.com/RSASHA256/26186 (KSK) + + No errors found + + Checking scheduled ZSK events for zone example.com, algorithm RSASHA256... + Wed Jun 17 11:03:18 UTC 2020: + Publish: example.com/RSASHA256/31168 (ZSK) + Activate: example.com/RSASHA256/31168 (ZSK) + Sun Aug 16 11:03:18 UTC 2020: + Publish: example.com/RSASHA256/24199 (ZSK) + + Ignoring events after Sun Aug 16 11:47:24 UTC 2020 + + No errors found + +The ``-d 2h`` and ``-m 1d`` on the command line specify the maximum TTL +for the DNSKEYs and other resource records in the zone: in this example +two hours and one day, respectively. ``dnssec-coverage`` needs this +information when it checks that the zones will remain secure through key +rolls. + +.. _advanced_discussions_automatic_dnssec-policy: + +Fully Automatic Signing With ``dnssec-policy`` +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The latest development in DNSSEC key management appeared with BIND 9.16, +and is the full integration of key management into ``named``. Managing +the signing process and rolling of these keys has been described in +:ref:`easy_start_guide_for_authoritative_servers` and is not +repeated here. A few points are worth noting, though: + +- The ``dnssec-policy`` statement in the ``named`` configuration file + describes all aspects of the DNSSEC policy, including the signing. + With ``dnssec-keymgr``, this is split between two configuration files + and two programs. + +- The ``dnssec-policy`` statement requires to zone to use dynamic DNS, + or that ``inline-signing`` is enabled. + +- It is possible to manage some zones served by an instance of BIND + through ``dnssec-policy`` and others through ``dnssec-keymgr``, but + this is not recommended. Although it should work, if you + modify the configuration files and inadvertently specify a zone to be + managed by both systems, BIND will not operate properly. + +.. _advanced_discussions_manual_key_management_and_signing: + +Manual Signing +^^^^^^^^^^^^^^ + +Manual signing of a zone was the first method of signing introduced into +BIND and offers, as the name suggests, no automation. The user must +handle everything: create the keys, sign the zone file with them, load +the signed zone, periodically re-sign the zone, and manage key rolls, +including interaction with the parent. A user certainly can do all this, +but why not use one of the automated methods? Nevertheless, it may +be useful for test purposes, so we cover it briefly here. + +BIND 9 ships with several tools that are used in +this process, which are explained in more detail below. In all cases, +the ``-h`` option prints a full list of parameters. Note that the DNSSEC +tools require the keyset files to be in the working directory or the +directory specified by the ``-d`` option. + +The first step is to create the keys as described in :ref:`generate_keys`. + +Then, edit the zone file to make sure the proper DNSKEY entries are included. +The public keys should be inserted into the zone file by +including the ``.key`` files using ``$INCLUDE`` statements. + +Finally, use the command ``dnssec-signzone``. +Any ``keyset`` files corresponding to secure sub-zones should be +present. The zone signer generates ``NSEC``, ``NSEC3``, and ``RRSIG`` +records for the zone, as well as ``DS`` for the child zones if +``-g`` is specified. If +``-g`` is not specified, then DS RRsets for the +secure child zones need to be added manually. + +By default, all zone keys which have an available private key are used +to generate signatures. The following command signs the zone, assuming +it is in a file called ``zone.child.example``, using manually specified keys: + +.. code-block:: console + + # cd /etc/bind/keys/example.com/ + # dnssec-signzone -t -N INCREMENT -o example.com -f /etc/bind/db/example.com.signed.db \ + /etc/bind/db/example.com.db Kexample.com.+013+17694.key Kexample.com.+013+06817.key + Verifying the zone using the following algorithms: ECDSAP256SHA256. + Zone fully signed: + Algorithm: ECDSAP256SHA256: KSKs: 1 active, 0 stand-by, 0 revoked + ZSKs: 1 active, 0 stand-by, 0 revoked + /etc/bind/db/example.com.signed.db + Signatures generated: 17 + Signatures retained: 0 + Signatures dropped: 0 + Signatures successfully verified: 0 + Signatures unsuccessfully verified: 0 + Signing time in seconds: 0.046 + Signatures per second: 364.634 + Runtime in seconds: 0.055 + +The -o switch explicitly defines the domain name (``example.com`` in +this case), while the -f switch specifies the output file name. The second line +has three parameters: the unsigned zone name +(``/etc/bind/db/example.com.db``), the ZSK file name, and the KSK file name. This +also generates a plain text file ``/etc/bind/db/example.com.signed.db``, +which can be manually verified for correctness. + +``dnssec-signzone`` also produces keyset and dsset files. These are used +to provide the parent zone administrators with the ``DNSKEY`` records (or their +corresponding ``DS`` records) that are the secure entry point to the zone. + +Finally, you'll need to update ``named.conf`` to load the signed version +of the zone, which looks something like this: + +.. code-block:: none + + zone "example.com" IN { + type primary; + file "db/example.com.signed.db"; + }; + +Once the ``rndc reconfig`` command is issued, BIND serves a signed +zone. The file ``dsset-example.com`` (created by ``dnssec-signzone`` +when it signed the ``example.com`` zone) contains the DS record for the +zone's KSK. You will need to pass that to the administrator of the parent +zone, to be placed in the zone. + +Since this is a manual process, you will need to re-sign periodically, +as well as every time the zone +data changes. You will also need to manually roll the keys by adding and +removing DNSKEY records (and interacting with the parent) at the +appropriate times. + +.. [#] + The dates can also be modified using an editor, but that is likely to + be more error-prone than using ``dnssec-settime``. + +.. [#] + Only one key file - for either a KSK or ZSK - is needed to signal the + presence of the zone. ``dnssec-keygen`` creates files of both + types as needed. diff --git a/doc/dnssec-guide/troubleshooting.rst b/doc/dnssec-guide/troubleshooting.rst new file mode 100644 index 0000000..cdc40cc --- /dev/null +++ b/doc/dnssec-guide/troubleshooting.rst @@ -0,0 +1,589 @@ +.. Copyright (C) Internet Systems Consortium, Inc. ("ISC") +.. +.. SPDX-License-Identifier: MPL-2.0 +.. +.. This Source Code Form is subject to the terms of the Mozilla Public +.. License, v. 2.0. If a copy of the MPL was not distributed with this +.. file, you can obtain one at https://mozilla.org/MPL/2.0/. +.. +.. See the COPYRIGHT file distributed with this work for additional +.. information regarding copyright ownership. + +.. _dnssec_troubleshooting: + +Basic DNSSEC Troubleshooting +---------------------------- + +In this chapter, we cover some basic troubleshooting +techniques, some common DNSSEC symptoms, and their causes and solutions. This +is not a comprehensive "how to troubleshoot any DNS or DNSSEC problem" +guide, because that could easily be an entire book by itself. + +.. _troubleshooting_query_path: + +Query Path +~~~~~~~~~~ + +The first step in troubleshooting DNS or DNSSEC should be to +determine the query path. Whenever you are working with a DNS-related issue, it is +always a good idea to determine the exact query path to identify the +origin of the problem. + +End clients, such as laptop computers or mobile phones, are configured +to talk to a recursive name server, and the recursive name server may in +turn forward requests on to other recursive name servers before arriving at the +authoritative name server. The giveaway is the presence of the +Authoritative Answer (``aa``) flag in a query response: when present, we know we are talking +to the authoritative server; when missing, we are talking to a recursive +server. The example below shows an answer to a query for +``www.example.com`` without the Authoritative Answer flag: + +:: + + $ dig @10.53.0.3 www.example.com A + + ; <<>> DiG 9.16.0 <<>> @10.53.0.3 www.example.com a + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62714 + ;; flags: qr rd ra ad; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1 + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags:; udp: 4096 + ; COOKIE: c823fe302625db5b010000005e722b504d81bb01c2227259 (good) + ;; QUESTION SECTION: + ;www.example.com. IN A + + ;; ANSWER SECTION: + www.example.com. 60 IN A 10.1.0.1 + + ;; Query time: 3 msec + ;; SERVER: 10.53.0.3#53(10.53.0.3) + ;; WHEN: Wed Mar 18 14:08:16 GMT 2020 + ;; MSG SIZE rcvd: 88 + +Not only do we not see the ``aa`` flag, we see an ``ra`` +flag, which indicates Recursion Available. This indicates that the +server we are talking to (10.53.0.3 in this example) is a recursive name +server: although we were able to get an answer for +``www.example.com``, we know that the answer came from somewhere else. + +If we query the authoritative server directly, we get: + +:: + + $ dig @10.53.0.2 www.example.com A + + ; <<>> DiG 9.16.0 <<>> @10.53.0.2 www.example.com a + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39542 + ;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1 + ;; WARNING: recursion requested but not available + ... + +The ``aa`` flag tells us that we are now talking to the +authoritative name server for ``www.example.com``, and that this is not a +cached answer it obtained from some other name server; it served this +answer to us right from its own database. In fact, +the Recursion Available (``ra``) flag is not present, which means this +name server is not configured to perform recursion (at least not for +this client), so it could not have queried another name server to get +cached results. + +.. _troubleshooting_visible_symptoms: + +Visible DNSSEC Validation Symptoms +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +After determining the query path, it is necessary to +determine whether the problem is actually related to DNSSEC +validation. You can use the ``+cd`` flag in ``dig`` to disable +validation, as described in +:ref:`how_do_i_know_validation_problem`. + +When there is indeed a DNSSEC validation problem, the visible symptoms, +unfortunately, are very limited. With DNSSEC validation enabled, if a +DNS response is not fully validated, it results in a generic +SERVFAIL message, as shown below when querying against a recursive name +server at 192.168.1.7: + +:: + + $ dig @10.53.0.3 www.example.org. A + + ; <<>> DiG 9.16.0 <<>> @10.53.0.3 www.example.org A + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 28947 + ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1 + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags:; udp: 4096 + ; COOKIE: d1301968aca086ad010000005e723a7113603c01916d136b (good) + ;; QUESTION SECTION: + ;www.example.org. IN A + + ;; Query time: 3 msec + ;; SERVER: 10.53.0.3#53(10.53.0.3) + ;; WHEN: Wed Mar 18 15:12:49 GMT 2020 + ;; MSG SIZE rcvd: 72 + +With ``delv``, a "resolution failed" message is output instead: + +:: + + $ delv @10.53.0.3 www.example.org. A +rtrace + ;; fetch: www.example.org/A + ;; resolution failed: SERVFAIL + +BIND 9 logging features may be useful when trying to identify +DNSSEC errors. + +.. _troubleshooting_logging: + +Basic Logging +~~~~~~~~~~~~~ + +DNSSEC validation error messages show up in ``syslog`` as a +query error by default. Here is an example of what it may look like: + +:: + + validating www.example.org/A: no valid signature found + RRSIG failed to verify resolving 'www.example.org/A/IN': 10.53.0.2#53 + +Usually, this level of error logging is sufficient. +Debug logging, described in +:ref:`troubleshooting_logging_debug`, gives information on how +to get more details about why DNSSEC validation may have +failed. + +.. _troubleshooting_logging_debug: + +BIND DNSSEC Debug Logging +~~~~~~~~~~~~~~~~~~~~~~~~~ + +A word of caution: before you enable debug logging, be aware that this +may dramatically increase the load on your name servers. Enabling debug +logging is thus not recommended for production servers. + +With that said, sometimes it may become necessary to temporarily enable +BIND debug logging to see more details of how and whether DNSSEC is +validating. DNSSEC-related messages are not recorded in ``syslog`` by default, +even if query log is enabled; only DNSSEC errors show up in ``syslog``. + +The example below shows how to enable debug level 3 (to see full DNSSEC +validation messages) in BIND 9 and have it sent to ``syslog``: + +:: + + logging { + channel dnssec_log { + syslog daemon; + severity debug 3; + print-category yes; + }; + category dnssec { dnssec_log; }; + }; + +The example below shows how to log DNSSEC messages to their own file +(here, ``/var/log/dnssec.log``): + +:: + + logging { + channel dnssec_log { + file "/var/log/dnssec.log"; + severity debug 3; + }; + category dnssec { dnssec_log; }; + }; + +After turning on debug logging and restarting BIND, a large +number of log messages appear in +``syslog``. The example below shows the log messages as a result of +successfully looking up and validating the domain name ``ftp.isc.org``. + +:: + + validating ./NS: starting + validating ./NS: attempting positive response validation + validating ./DNSKEY: starting + validating ./DNSKEY: attempting positive response validation + validating ./DNSKEY: verify rdataset (keyid=20326): success + validating ./DNSKEY: marking as secure (DS) + validating ./NS: in validator_callback_dnskey + validating ./NS: keyset with trust secure + validating ./NS: resuming validate + validating ./NS: verify rdataset (keyid=33853): success + validating ./NS: marking as secure, noqname proof not needed + validating ftp.isc.org/A: starting + validating ftp.isc.org/A: attempting positive response validation + validating isc.org/DNSKEY: starting + validating isc.org/DNSKEY: attempting positive response validation + validating isc.org/DS: starting + validating isc.org/DS: attempting positive response validation + validating org/DNSKEY: starting + validating org/DNSKEY: attempting positive response validation + validating org/DS: starting + validating org/DS: attempting positive response validation + validating org/DS: keyset with trust secure + validating org/DS: verify rdataset (keyid=33853): success + validating org/DS: marking as secure, noqname proof not needed + validating org/DNSKEY: in validator_callback_ds + validating org/DNSKEY: dsset with trust secure + validating org/DNSKEY: verify rdataset (keyid=9795): success + validating org/DNSKEY: marking as secure (DS) + validating isc.org/DS: in fetch_callback_dnskey + validating isc.org/DS: keyset with trust secure + validating isc.org/DS: resuming validate + validating isc.org/DS: verify rdataset (keyid=33209): success + validating isc.org/DS: marking as secure, noqname proof not needed + validating isc.org/DNSKEY: in validator_callback_ds + validating isc.org/DNSKEY: dsset with trust secure + validating isc.org/DNSKEY: verify rdataset (keyid=7250): success + validating isc.org/DNSKEY: marking as secure (DS) + validating ftp.isc.org/A: in fetch_callback_dnskey + validating ftp.isc.org/A: keyset with trust secure + validating ftp.isc.org/A: resuming validate + validating ftp.isc.org/A: verify rdataset (keyid=27566): success + validating ftp.isc.org/A: marking as secure, noqname proof not needed + +Note that these log messages indicate that the chain of trust has been +established and ``ftp.isc.org`` has been successfully validated. + +If validation had failed, you would see log messages indicating errors. +We cover some of the most validation problems in the next section. + +.. _troubleshooting_common_problems: + +Common Problems +~~~~~~~~~~~~~~~ + +.. _troubleshooting_security_lameness: + +Security Lameness +^^^^^^^^^^^^^^^^^ + +Similar to lame delegation in traditional DNS, security lameness refers to the +condition when the parent zone holds a set of DS records that point to +something that does not exist in the child zone. As a result, +the entire child zone may "disappear," having been marked as bogus by +validating resolvers. + +Below is an example attempting to resolve the A record for a test domain +name ``www.example.net``. From the user's perspective, as described in +:ref:`how_do_i_know_validation_problem`, only a SERVFAIL +message is returned. On the validating resolver, we see the +following messages in ``syslog``: + +:: + + named[126063]: validating example.net/DNSKEY: no valid signature found (DS) + named[126063]: no valid RRSIG resolving 'example.net/DNSKEY/IN': 10.53.0.2#53 + named[126063]: broken trust chain resolving 'www.example.net/A/IN': 10.53.0.2#53 + +This gives us a hint that it is a broken trust chain issue. Let's take a +look at the DS records that are published for the zone (with the keys +shortened for ease of display): + +:: + + $ dig @10.53.0.3 example.net. DS + + ; <<>> DiG 9.16.0 <<>> @10.53.0.3 example.net DS + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 59602 + ;; flags: qr rd ra ad; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1 + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags:; udp: 4096 + ; COOKIE: 7026d8f7c6e77e2a010000005e735d7c9d038d061b2d24da (good) + ;; QUESTION SECTION: + ;example.net. IN DS + + ;; ANSWER SECTION: + example.net. 256 IN DS 14956 8 2 9F3CACD...D3E3A396 + + ;; Query time: 0 msec + ;; SERVER: 10.53.0.3#53(10.53.0.3) + ;; WHEN: Thu Mar 19 11:54:36 GMT 2020 + ;; MSG SIZE rcvd: 116 + +Next, we query for the DNSKEY and RRSIG of ``example.net`` to see if +there's anything wrong. Since we are having trouble validating, we +can use the ``+cd`` option to temporarily disable checking and return +results, even though they do not pass the validation tests. The +``+multiline`` option tells ``dig`` to print the type, algorithm type, +and key id for DNSKEY records. Again, +some long strings are shortened for ease of display: + +:: + + $ dig @10.53.0.3 example.net. DNSKEY +dnssec +cd +multiline + + ; <<>> DiG 9.16.0 <<>> @10.53.0.3 example.net DNSKEY +cd +multiline +dnssec + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 42980 + ;; flags: qr rd ra cd; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1 + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags: do; udp: 4096 + ; COOKIE: 4b5e7c88b3680c35010000005e73722057551f9f8be1990e (good) + ;; QUESTION SECTION: + ;example.net. IN DNSKEY + + ;; ANSWER SECTION: + example.net. 287 IN DNSKEY 256 3 8 ( + AwEAAbu3NX...ADU/D7xjFFDu+8WRIn + ) ; ZSK; alg = RSASHA256 ; key id = 35328 + example.net. 287 IN DNSKEY 257 3 8 ( + AwEAAbKtU1...PPP4aQZTybk75ZW+uL + 6OJMAF63NO0s1nAZM2EWAVasbnn/X+J4N2rLuhk= + ) ; KSK; alg = RSASHA256 ; key id = 27247 + example.net. 287 IN RRSIG DNSKEY 8 2 300 ( + 20811123173143 20180101000000 27247 example.net. + Fz1sjClIoF...YEjzpAWuAj9peQ== ) + example.net. 287 IN RRSIG DNSKEY 8 2 300 ( + 20811123173143 20180101000000 35328 example.net. + seKtUeJ4/l...YtDc1rcXTVlWIOw= ) + + ;; Query time: 0 msec + ;; SERVER: 10.53.0.3#53(10.53.0.3) + ;; WHEN: Thu Mar 19 13:22:40 GMT 2020 + ;; MSG SIZE rcvd: 962 + +Here is the problem: the parent zone is telling the world that +``example.net`` is using the key 14956, but the authoritative server +indicates that it is using keys 27247 and 35328. There are several +potential causes for this mismatch: one possibility is that a malicious +attacker has compromised one side and changed the data. A more likely +scenario is that the DNS administrator for the child zone did not upload +the correct key information to the parent zone. + +.. _troubleshooting_incorrect_time: + +Incorrect Time +^^^^^^^^^^^^^^ + +In DNSSEC, every record comes with at least one RRSIG, and each RRSIG +contains two timestamps: one indicating when it becomes valid, and +one when it expires. If the validating resolver's current system time does +not fall within the two RRSIG timestamps, error messages +appear in the BIND debug log. + +The example below shows a log message when the RRSIG appears to have +expired. This could mean the validating resolver system time is +incorrectly set too far in the future, or the zone administrator has not +kept up with RRSIG maintenance. + +:: + + validating example.com/DNSKEY: verify failed due to bad signature (keyid=19036): RRSIG has expired + +The log below shows that the RRSIG validity period has not yet begun. This could mean +the validation resolver's system time is incorrectly set too far in the past, or +the zone administrator has incorrectly generated signatures for this +domain name. + +:: + + validating example.com/DNSKEY: verify failed due to bad signature (keyid=4521): RRSIG validity period has not begun + +.. _troubleshooting_unable_to_load_keys: + +Unable to Load Keys +^^^^^^^^^^^^^^^^^^^ + +This is a simple yet common issue. If the key files are present but +unreadable by ``named`` for some reason, the ``syslog`` returns clear error +messages, as shown below: + +:: + + named[32447]: zone example.com/IN (signed): reconfiguring zone keys + named[32447]: dns_dnssec_findmatchingkeys: error reading key file Kexample.com.+008+06817.private: permission denied + named[32447]: dns_dnssec_findmatchingkeys: error reading key file Kexample.com.+008+17694.private: permission denied + named[32447]: zone example.com/IN (signed): next key event: 27-Nov-2014 20:04:36.521 + +However, if no keys are found, the error is not as obvious. Below shows +the ``syslog`` messages after executing ``rndc +reload`` with the key files missing from the key directory: + +:: + + named[32516]: received control channel command 'reload' + named[32516]: loading configuration from '/etc/bind/named.conf' + named[32516]: reading built-in trusted keys from file '/etc/bind/bind.keys' + named[32516]: using default UDP/IPv4 port range: [1024, 65535] + named[32516]: using default UDP/IPv6 port range: [1024, 65535] + named[32516]: sizing zone task pool based on 6 zones + named[32516]: the working directory is not writable + named[32516]: reloading configuration succeeded + named[32516]: reloading zones succeeded + named[32516]: all zones loaded + named[32516]: running + named[32516]: zone example.com/IN (signed): reconfiguring zone keys + named[32516]: zone example.com/IN (signed): next key event: 27-Nov-2014 20:07:09.292 + +This happens to look exactly the same as if the keys were present and +readable, and appears to indicate that ``named`` loaded the keys and signed the zone. It +even generates the internal (raw) files: + +:: + + # cd /etc/bind/db + # ls + example.com.db example.com.db.jbk example.com.db.signed + +If ``named`` really loaded the keys and signed the zone, you should see +the following files: + +:: + + # cd /etc/bind/db + # ls + example.com.db example.com.db.jbk example.com.db.signed example.com.db.signed.jnl + +So, unless you see the ``*.signed.jnl`` file, your zone has not been +signed. + +.. _troubleshooting_invalid_trust_anchors: + +Invalid Trust Anchors +^^^^^^^^^^^^^^^^^^^^^ + +In most cases, you never need to explicitly configure trust +anchors. ``named`` supplies the current root trust anchor and, +with the default setting of ``dnssec-validation``, updates it on the +infrequent occasions when it is changed. + +However, in some circumstances you may need to explicitly configure +your own trust anchor. As we saw in the :ref:`trust_anchors_description` +section, whenever a DNSKEY is received by the validating resolver, it is +compared to the list of keys the resolver explicitly trusts to see if +further action is needed. If the two keys match, the validating resolver +stops performing further verification and returns the answer(s) as +validated. + +But what if the key file on the validating resolver is misconfigured or +missing? Below we show some examples of log messages when things are not +working properly. + +First of all, if the key you copied is malformed, BIND does not even +start and you will likely find this error message in syslog: + +:: + + named[18235]: /etc/bind/named.conf.options:29: bad base64 encoding + named[18235]: loading configuration: failure + +If the key is a valid base64 string but the key algorithm is incorrect, +or if the wrong key is installed, the first thing you will notice is +that virtually all of your DNS lookups result in SERVFAIL, even when +you are looking up domain names that have not been DNSSEC-enabled. Below +shows an example of querying a recursive server 10.53.0.3: + +:: + + $ dig @10.53.0.3 www.example.com. A + + ; <<>> DiG 9.16.0 <<>> @10.53.0.3 www.example.org A +dnssec + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 29586 + ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1 + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags: do; udp: 4096 + ; COOKIE: ee078fc321fa1367010000005e73a58bf5f205ca47e04bed (good) + ;; QUESTION SECTION: + ;www.example.org. IN A + +``delv`` shows a similar result: + +:: + + $ delv @192.168.1.7 www.example.com. +rtrace + ;; fetch: www.example.com/A + ;; resolution failed: SERVFAIL + +The next symptom you see is in the DNSSEC log messages: + +:: + + managed-keys-zone: DNSKEY set for zone '.' could not be verified with current keys + validating ./DNSKEY: starting + validating ./DNSKEY: attempting positive response validation + validating ./DNSKEY: no DNSKEY matching DS + validating ./DNSKEY: no DNSKEY matching DS + validating ./DNSKEY: no valid signature found (DS) + +These errors are indications that there are problems with the trust +anchor. + +.. _troubleshooting_nta: + +Negative Trust Anchors +~~~~~~~~~~~~~~~~~~~~~~ + +BIND 9.11 introduced Negative Trust Anchors (NTAs) as a means to +*temporarily* disable DNSSEC validation for a zone when you know that +the zone's DNSSEC is misconfigured. + +NTAs are added using the ``rndc`` command, e.g.: + +:: + + $ rndc nta example.com + Negative trust anchor added: example.com/_default, expires 19-Mar-2020 19:57:42.000 + + +The list of currently configured NTAs can also be examined using +``rndc``, e.g.: + +:: + + $ rndc nta -dump + example.com/_default: expiry 19-Mar-2020 19:57:42.000 + + +The default lifetime of an NTA is one hour, although by default, BIND +polls the zone every five minutes to see if the zone correctly +validates, at which point the NTA automatically expires. Both the +default lifetime and the polling interval may be configured via +``named.conf``, and the lifetime can be overridden on a per-zone basis +using the ``-lifetime duration`` parameter to ``rndc nta``. Both timer +values have a permitted maximum value of one week. + +.. _troubleshooting_nsec3: + +NSEC3 Troubleshooting +~~~~~~~~~~~~~~~~~~~~~ + +BIND includes a tool called ``nsec3hash`` that runs through the same +steps as a validating resolver, to generate the correct hashed name +based on NSEC3PARAM parameters. The command takes the following +parameters in order: salt, algorithm, iterations, and domain. For +example, if the salt is 1234567890ABCDEF, hash algorithm is 1, and +iteration is 10, to get the NSEC3-hashed name for ``www.example.com`` we +would execute a command like this: + +:: + + $ nsec3hash 1234567890ABCEDF 1 10 www.example.com + RN7I9ME6E1I6BDKIP91B9TCE4FHJ7LKF (salt=1234567890ABCEDF, hash=1, iterations=10) + +Zero-length salt can be specified as ``-``. + +While it is unlikely you would construct a rainbow table of your own +zone data, this tool may be useful when troubleshooting NSEC3 problems. diff --git a/doc/dnssec-guide/validation.rst b/doc/dnssec-guide/validation.rst new file mode 100644 index 0000000..2830b98 --- /dev/null +++ b/doc/dnssec-guide/validation.rst @@ -0,0 +1,864 @@ +.. Copyright (C) Internet Systems Consortium, Inc. ("ISC") +.. +.. SPDX-License-Identifier: MPL-2.0 +.. +.. This Source Code Form is subject to the terms of the Mozilla Public +.. License, v. 2.0. If a copy of the MPL was not distributed with this +.. file, you can obtain one at https://mozilla.org/MPL/2.0/. +.. +.. See the COPYRIGHT file distributed with this work for additional +.. information regarding copyright ownership. + +.. _DNSSEC_validation: + +Validation +---------- + +.. _easy_start_guide_for_recursive_servers: + +Easy-Start Guide for Recursive Servers +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +This section provides the basic information needed to set up a +working DNSSEC-aware recursive server, also known as a validating +resolver. A validating resolver performs validation for each remote +response received, following the chain of trust to verify that the answers it +receives are legitimate, through the use of public key cryptography and +hashing functions. + +.. _enabling_validation: + +Enabling DNSSEC Validation +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +So how do we turn on DNSSEC validation? It turns out that you may not need +to reconfigure your name server at all, since the most recent versions of BIND 9 - +including packages and distributions - have shipped with DNSSEC validation +enabled by default. Before making any configuration changes, check +whether you already have DNSSEC validation enabled by following the steps +described in :ref:`how_to_test_recursive_server`. + +In earlier versions of BIND, including 9.11-ESV, DNSSEC +validation must be explicitly enabled. To do this, you only need to +add one line to the ``options`` section of your configuration file: + +:: + + options { + ... + dnssec-validation auto; + ... + }; + +Restart ``named`` or run ``rndc reconfig``, and your recursive server is +now happily validating each DNS response. If this does not work for you, +you may have some other network-related configurations that need to be +adjusted. Take a look at :ref:`network_requirements` to make sure your network +is ready for DNSSEC. + +.. _effect_of_enabling_validation: + +Effects of Enabling DNSSEC Validation +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Once DNSSEC validation is enabled, any DNS response that does not pass +the validation checks results in a failure to resolve the domain name +(often a SERVFAIL status seen by the client). If everything has +been configured properly, this is the correct result; it means that an end user has +been protected against a malicious attack. + +However, if there is a DNSSEC configuration issue (sometimes outside of +the administrator's control), a specific name or sometimes entire +domains may "disappear" from the DNS, and become unreachable +through that resolver. For the end user, the issue may manifest itself +as name resolution being slow or failing altogether; some parts of a URL +not loading; or the web browser returning an error message indicating +that the page cannot be displayed. For example, if root name +servers were misconfigured with the wrong information about ``.org``, it +could cause all validation for ``.org`` domains to fail. To end +users, it would appear that all ``.org`` web +sites were out of service [#]_. Should you encounter DNSSEC-related problems, don't be +tempted to disable validation; there is almost certainly a solution that +leaves validation enabled. A basic troubleshooting guide can be found in +:ref:`dnssec_troubleshooting`. + +.. [#] + Of course, something like this could happen for reasons other than + DNSSEC: for example, the root publishing the wrong addresses for the + ``.org`` nameservers. + +.. _how_to_test_recursive_server: + +So You Think You Are Validating (How To Test A Recursive Server) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Now that you have reconfigured your recursive server and +restarted it, how do you know that your recursive name server is +actually verifying each DNS query? There are several ways to check, and +we've listed a few of them below. + +.. _using_web_based_tests_to_verify: + +Using Web-Based Tools to Verify +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +For most people, the simplest way to check if a recursive name server +is indeed validating DNS queries is to use one of the many web-based +tools available. + +Configure your client computer to use the newly reconfigured recursive +server for DNS resolution; then use one of these web-based tests to +confirm that it is in fact validating DNS responses. + +- `Internet.nl <https://en.conn.internet.nl/connection/>`__ + +- `DNSSEC or Not (VeriSign) <https://www.dnssec-or-not.com/>`__ + +.. _using_dig_to_verify: + +Using ``dig`` to Verify +^^^^^^^^^^^^^^^^^^^^^^^ + +Web-based DNSSEC-verification tools often employ JavaScript. If you don't trust the +JavaScript magic that the web-based tools rely on, you can take matters +into your own hands and use a command-line DNS tool to check your +validating resolver yourself. + +While ``nslookup`` is popular, partly because it comes pre-installed on +most systems, it is not DNSSEC-aware. ``dig``, on the other hand, fully +supports the DNSSEC standard and comes as a part of BIND. If you do not +have ``dig`` already installed on your system, install it by downloading +it from ISC's `website <https://www.isc.org/download>`__. ISC provides pre-compiled +Windows versions on its website. + +``dig`` is a flexible tool for interrogating DNS name servers. It +performs DNS lookups and displays the answers that are returned from the +name servers that were queried. Most seasoned DNS administrators use +``dig`` to troubleshoot DNS problems because of its flexibility, ease of +use, and clarity of output. + +The example below shows how to use ``dig`` to query the name server 10.53.0.1 +for the A record for ``ftp.isc.org`` when DNSSEC validation is enabled +(i.e. the default). The address 10.53.0.1 is only used as an example; +replace it with the actual address or host name of your +recursive name server. + +:: + + $ dig @10.53.0.1 ftp.isc.org. A +dnssec +multiline + + ; <<>> DiG 9.16.0 <<>> @10.53.0.1 ftp.isc.org a +dnssec +multiline + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 48742 + ;; flags: qr rd ra ad; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1 + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags: do; udp: 4096 + ; COOKIE: 29a9705c2160b08c010000005e67a4a102b9ae079c1b24c8 (good) + ;; QUESTION SECTION: + ;ftp.isc.org. IN A + + ;; ANSWER SECTION: + ftp.isc.org. 300 IN A 149.20.1.49 + ftp.isc.org. 300 IN RRSIG A 13 3 300 ( + 20200401191851 20200302184340 27566 isc.org. + e9Vkb6/6aHMQk/t23Im71ioiDUhB06sncsduoW9+Asl4 + L3TZtpLvZ5+zudTJC2coI4D/D9AXte1cD6FV6iS6PQ== ) + + ;; Query time: 452 msec + ;; SERVER: 10.53.0.1#53(10.53.0.1) + ;; WHEN: Tue Mar 10 14:30:57 GMT 2020 + ;; MSG SIZE rcvd: 187 + +The important detail in this output is the presence of the ``ad`` flag +in the header. This signifies that BIND has retrieved all related DNSSEC +information related to the target of the query (``ftp.isc.org``) and that +the answer received has passed the validation process described in +:ref:`how_are_answers_verified`. We can have confidence in the +authenticity and integrity of the answer, that ``ftp.isc.org`` really +points to the IP address 149.20.1.49, and that it was not a spoofed answer +from a clever attacker. + +Unlike earlier versions of BIND, the current versions of BIND always +request DNSSEC records (by setting the ``do`` bit in the query they make +to upstream servers), regardless of DNSSEC settings. However, with +validation disabled, the returned signature is not checked. This can be +seen by explicitly disabling DNSSEC validation. To do this, add the line +``dnssec-validation no;`` to the "options" section of the configuration +file, i.e.: + +:: + + options { + ... + dnssec-validation no; + ... + }; + +If the server is restarted (to ensure a clean cache) and the same +``dig`` command executed, the result is very similar: + +:: + + $ dig @10.53.0.1 ftp.isc.org. A +dnssec +multiline + + ; <<>> DiG 9.16.0 <<>> @10.53.0.1 ftp.isc.org a +dnssec +multiline + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39050 + ;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1 + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags: do; udp: 4096 + ; COOKIE: a8dc9d1b9ec45e75010000005e67a8a69399741fdbe126f2 (good) + ;; QUESTION SECTION: + ;ftp.isc.org. IN A + + ;; ANSWER SECTION: + ftp.isc.org. 300 IN A 149.20.1.49 + ftp.isc.org. 300 IN RRSIG A 13 3 300 ( + 20200401191851 20200302184340 27566 isc.org. + e9Vkb6/6aHMQk/t23Im71ioiDUhB06sncsduoW9+Asl4 + L3TZtpLvZ5+zudTJC2coI4D/D9AXte1cD6FV6iS6PQ== ) + + ;; Query time: 261 msec + ;; SERVER: 10.53.0.1#53(10.53.0.1) + ;; WHEN: Tue Mar 10 14:48:06 GMT 2020 + ;; MSG SIZE rcvd: 187 + +However, this time there is no ``ad`` flag in the header. Although +``dig`` is still returning the DNSSEC-related resource records, it is +not checking them, and thus cannot vouch for the authenticity of the answer. +If you do carry out this test, remember to re-enable DNSSEC validation +(by removing the ``dnssec-validation no;`` line from the configuration +file) before continuing. + +.. _verifying_protection_from_bad_domains: + +Verifying Protection From Bad Domain Names +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +It is also important to make sure that DNSSEC is protecting your network from +domain names that fail to validate; such failures could be caused by +attacks on your system, attempting to get it to accept false DNS +information. Validation could fail for a number of reasons: maybe the +answer doesn't verify because it's a spoofed response; maybe the +signature was a replayed network attack that has expired; or maybe the +child zone has been compromised along with its keys, and the parent +zone's information tells us that things don't add up. There is a +domain name specifically set up to fail DNSSEC validation, +``www.dnssec-failed.org``. + +With DNSSEC validation enabled (the default), an attempt to look up that +name fails: + +:: + + $ dig @10.53.0.1 www.dnssec-failed.org. A + + ; <<>> DiG 9.16.0 <<>> @10.53.0.1 www.dnssec-failed.org. A + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 22667 + ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1 + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags:; udp: 4096 + ; COOKIE: 69c3083144854587010000005e67bb57f5f90ff2688e455d (good) + ;; QUESTION SECTION: + ;www.dnssec-failed.org. IN A + + ;; Query time: 2763 msec + ;; SERVER: 10.53.0.1#53(10.53.0.1) + ;; WHEN: Tue Mar 10 16:07:51 GMT 2020 + ;; MSG SIZE rcvd: 78 + +On the other hand, if DNSSEC validation is disabled (by adding the +statement ``dnssec-validation no;`` to the ``options`` clause in the +configuration file), the lookup succeeds: + +:: + + $ dig @10.53.0.1 www.dnssec-failed.org. A + + ; <<>> DiG 9.16.0 <<>> @10.53.0.1 www.dnssec-failed.org. A + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 54704 + ;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1 + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags:; udp: 4096 + ; COOKIE: 251eee58208917f9010000005e67bb6829f6dabc5ae6b7b9 (good) + ;; QUESTION SECTION: + ;www.dnssec-failed.org. IN A + + ;; ANSWER SECTION: + www.dnssec-failed.org. 7200 IN A 68.87.109.242 + www.dnssec-failed.org. 7200 IN A 69.252.193.191 + + ;; Query time: 439 msec + ;; SERVER: 10.53.0.1#53(10.53.0.1) + ;; WHEN: Tue Mar 10 16:08:08 GMT 2020 + ;; MSG SIZE rcvd: 110 + +Do not be tempted to disable DNSSEC validation just because some names +are failing to resolve. Remember, DNSSEC protects your DNS lookup from +hacking. The next section describes how to quickly check whether +the failure to successfully look up a name is due to a validation +failure. + +.. _how_do_i_know_validation_problem: + +How Do I Know I Have a Validation Problem? +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Since all DNSSEC validation failures result in a general ``SERVFAIL`` +message, how do we know if it was really a validation error? +Fortunately, there is a flag in ``dig``, (``+cd``, for "checking +disabled") which tells the server to disable DNSSEC validation. If +you receive a ``SERVFAIL`` message, re-run the query a second time +and set the ``+cd`` flag. If the query succeeds with ``+cd``, but +ends in ``SERVFAIL`` without it, you know you are dealing with a +validation problem. So using the previous example of +``www.dnssec-failed.org`` and with DNSSEC validation enabled in the +resolver: + +:: + + $ dig @10.53.0.1 www.dnssec-failed.org A +cd + + ; <<>> DiG 9.16.0 <<>> @10.53.0.1 www.dnssec-failed.org. A +cd + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62313 + ;; flags: qr rd ra cd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1 + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags:; udp: 4096 + ; COOKIE: 73ca1be3a74dd2cf010000005e67c8c8e6df64b519cd87fd (good) + ;; QUESTION SECTION: + ;www.dnssec-failed.org. IN A + + ;; ANSWER SECTION: + www.dnssec-failed.org. 7197 IN A 68.87.109.242 + www.dnssec-failed.org. 7197 IN A 69.252.193.191 + + ;; Query time: 0 msec + ;; SERVER: 10.53.0.1#53(10.53.0.1) + ;; WHEN: Tue Mar 10 17:05:12 GMT 2020 + ;; MSG SIZE rcvd: 110 + +For more information on troubleshooting, please see +:ref:`dnssec_troubleshooting`. + +.. _validation_easy_start_explained: + +Validation Easy Start Explained +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +In :ref:`easy_start_guide_for_recursive_servers`, we used one line +of configuration to turn on DNSSEC validation: the act of chasing down +signatures and keys, making sure they are authentic. Now we are going to +take a closer look at what DNSSEC validation actually does, and some other options. + +.. _dnssec_validation_explained: + +``dnssec-validation`` +^^^^^^^^^^^^^^^^^^^^^ + +:: + + options { + dnssec-validation auto; + }; + +This “auto” line enables automatic DNSSEC trust anchor configuration +using the ``managed-keys`` feature. In this case, no manual key +configuration is needed. There are three possible choices for the +``dnssec-validation`` option: + +- *yes*: DNSSEC validation is enabled, but a trust anchor must be + manually configured. No validation actually takes place until + at least one trusted key has been manually configured. + +- *no*: DNSSEC validation is disabled, and the recursive server behaves + in the "old-fashioned" way of performing insecure DNS lookups. + +- *auto*: DNSSEC validation is enabled, and a default trust anchor + (included as part of BIND 9) for the DNS root zone is used. This is the + default; BIND automatically does this if there is no + ``dnssec-validation`` line in the configuration file. + +Let's discuss the difference between *yes* and *auto*. If set to +*yes*, the trust anchor must be manually defined and maintained +using the ``trust-anchors`` statement (with either the ``static-key`` or +``static-ds`` modifier) in the configuration file; if set to +*auto* (the default, and as shown in the example), then no further +action should be required as BIND includes a copy [#]_ of the root key. +When set to *auto*, BIND automatically keeps the keys (also known as +trust anchors, discussed in :ref:`trust_anchors_description`) +up-to-date without intervention from the DNS administrator. + +We recommend using the default *auto* unless there is a good reason to +require a manual trust anchor. To learn more about trust anchors, +please refer to :ref:`trusted_keys_and_managed_keys`. + +.. _how_does_dnssec_change_dns_lookup_revisited: + +How Does DNSSEC Change DNS Lookup (Revisited)? +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Now you've enabled validation on your recursive name server and +verified that it works. What exactly changed? In +:ref:`how_does_dnssec_change_dns_lookup` we looked at a very +high-level, simplified version of the 12 steps of the DNSSEC validation process. Let's revisit +that process now and see what your validating resolver is doing in more +detail. Again, as an example we are looking up the A record for the +domain name ``www.isc.org`` (see :ref:`dnssec_12_steps`): + +1. The validating resolver queries the ``isc.org`` name servers for the + A record of ``www.isc.org``. This query has the ``DNSSEC + OK`` (``do``) bit set to 1, notifying the remote authoritative + server that DNSSEC answers are desired. + +2. Since the zone ``isc.org`` is signed, and its name servers are + DNSSEC-aware, it responds with the answer to the A record query plus + the RRSIG for the A record. + +3. The validating resolver queries for the DNSKEY for ``isc.org``. + +4. The ``isc.org`` name server responds with the DNSKEY and RRSIG + records. The DNSKEY is used to verify the answers received in #2. + +5. The validating resolver queries the parent (``.org``) for the DS + record for ``isc.org``. + +6. The ``.org`` name server is also DNSSEC-aware, so it responds with the + DS and RRSIG records. The DS record is used to verify the answers + received in #4. + +7. The validating resolver queries for the DNSKEY for ``.org``. + +8. The ``.org`` name server responds with its DNSKEY and RRSIG. The DNSKEY + is used to verify the answers received in #6. + +9. The validating resolver queries the parent (root) for the DS record + for ``.org``. + +10. The root name server, being DNSSEC-aware, responds with DS and RRSIG + records. The DS record is used to verify the answers received in #8. + +11. The validating resolver queries for the DNSKEY for root. + +12. The root name server responds with its DNSKEY and RRSIG. The DNSKEY is + used to verify the answers received in #10. + +After step #12, the validating resolver takes the DNSKEY received and +compares it to the key or keys it has configured, to decide whether +the received key can be trusted. We talk about these locally +configured keys, or trust anchors, in :ref:`trust_anchors_description`. + +With DNSSEC, every response includes not just the +answer, but a digital signature (RRSIG) as well, so the +validating resolver can verify the answer received. That is what we +look at in the next section, :ref:`how_are_answers_verified`. + +.. _how_are_answers_verified: + +How Are Answers Verified? +^^^^^^^^^^^^^^^^^^^^^^^^^ + +.. note:: + + Keep in mind, as you read this section, that although words like + "encryption" and "decryption" + are used here from time to time, DNSSEC does not provide privacy. + Public key cryptography is used to verify data *authenticity* (who + sent it) and data *integrity* (it did not change during transit), but + any eavesdropper can still see DNS requests and responses in + clear text, even when DNSSEC is enabled. + +So how exactly are DNSSEC answers verified? Let's first see how verifiable information is +generated. On the authoritative server, each DNS record (or message) is +run through a hash function, and this hashed value is then encrypted by a +private key. This encrypted hash value is the digital signature. + +.. figure:: ../dnssec-guide/img/signature-generation.png + :alt: Signature Generation + :width: 80.0% + + Signature Generation + +When the validating resolver queries for the resource record, it +receives both the plain-text message and the digital signature(s). The +validating resolver knows the hash function used (it is listed in the digital +signature record itself), so it can take the plain-text message and run +it through the same hash function to produce a hashed value, which we'll call +hash value X. The validating resolver can also obtain the public key +(published as DNSKEY records), decrypt the digital signature, and get +back the original hashed value produced by the authoritative server, +which we'll call hash value Y. If hash values X and Y are identical, and +the time is correct (more on what this means below), the answer is +verified, meaning this answer came from the authoritative server +(authenticity), and the content remained intact during transit +(integrity). + +.. figure:: ../dnssec-guide/img/signature-verification.png + :alt: Signature Verification + :width: 80.0% + + Signature Verification + +Take the A record ``ftp.isc.org``, for example. The plain text is: + +:: + + ftp.isc.org. 4 IN A 149.20.1.49 + +The digital signature portion is: + +:: + + ftp.isc.org. 300 IN RRSIG A 13 3 300 ( + 20200401191851 20200302184340 27566 isc.org. + e9Vkb6/6aHMQk/t23Im71ioiDUhB06sncsduoW9+Asl4 + L3TZtpLvZ5+zudTJC2coI4D/D9AXte1cD6FV6iS6PQ== ) + +When a validating resolver queries for the A record ``ftp.isc.org``, it +receives both the A record and the RRSIG record. It runs the A record +through a hash function (in this example, SHA256 as +indicated by the number 13, signifying ECDSAP256SHA256) and produces +hash value X. The resolver also fetches the appropriate DNSKEY record to +decrypt the signature, and the result of the decryption is hash value Y. + +But wait, there's more! Just because X equals Y doesn't mean everything +is good. We still have to look at the time. Remember we mentioned a +little earlier that we need to check if the time is correct? Look +at the two timestamps in our example above: + +- Signature Expiration: 20200401191851 + +- Signature Inception: 20200302184340 + +This tells us that this signature was generated UTC March 2nd, 2020, at +6:43:40 PM (20200302184340), and it is good until UTC April 1st, 2020, +7:18:51 PM (20200401191851). The validating resolver's current +system time needs to fall between these two timestamps. If it does not, the +validation fails, because it could be an attacker replaying an old +captured answer set from the past, or feeding us a crafted one with +incorrect future timestamps. + +If the answer passes both the hash value check and the timestamp check, it is +validated and the authenticated data (``ad``) bit is set, and the response +is sent to the client; if it does not verify, a SERVFAIL is returned to +the client. + +.. [#] + BIND technically includes two copies of the root key: one is in + ``bind.keys.h`` and is built into the executable, and one is in + ``bind.keys`` as a ``trust-anchors`` statement. The two copies of the + key are identical. + +.. _trust_anchors_description: + +Trust Anchors +~~~~~~~~~~~~~ + +A trust anchor is a key that is placed into a validating resolver, so +that the validator can verify the results of a given request with a +known or trusted public key (the trust anchor). A validating resolver +must have at least one trust anchor installed to perform DNSSEC +validation. + +.. _how_trust_anchors_are_used: + +How Trust Anchors are Used +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +In the section :ref:`how_does_dnssec_change_dns_lookup_revisited`, +we walked through the 12 steps of the DNSSEC lookup process. At the end +of the 12 steps, a critical comparison happens: the key received from +the remote server and the key we have on file are compared to see if we +trust it. The key we have on file is called a trust anchor, sometimes +also known as a trust key, trust point, or secure entry point. + +The 12-step lookup process describes the DNSSEC lookup in the ideal +world, where every single domain name is signed and properly delegated, +and where each validating resolver only needs to have one trust anchor - that +is, the root's public key. But there is no restriction that the +validating resolver must only have one trust anchor. In fact, in the +early stages of DNSSEC adoption, it was not unusual for a validating +resolver to have more than one trust anchor. + +For instance, before the root zone was signed (in July 2010), some +validating resolvers that wished to validate domain names in the ``.gov`` +zone needed to obtain and install the key for ``.gov``. A sample lookup +process for ``www.fbi.gov`` at that time would have been eight steps rather +than 12: + +.. figure:: ../dnssec-guide/img/dnssec-8-steps.png + :alt: DNSSEC Validation with ``.gov`` Trust Anchor + + +1. The validating resolver queried ``fbi.gov`` name server for the A + record of ``www.fbi.gov``. + +2. The FBI's name server responded with the answer and its RRSIG. + +3. The validating resolver queried the FBI's name server for its DNSKEY. + +4. The FBI's name server responded with the DNSKEY and its RRSIG. + +5. The validating resolver queried a ``.gov`` name server for the DS + record of ``fbi.gov``. + +6. The ``.gov`` name server responded with the DS record and the + associated RRSIG for ``fbi.gov``. + +7. The validating resolver queried the ``.gov`` name server for its DNSKEY. + +8. The ``.gov`` name server responded with its DNSKEY and the associated + RRSIG. + +This all looks very similar, except it's shorter than the 12 steps that +we saw earlier. Once the validating resolver receives the DNSKEY file in +#8, it recognizes that this is the manually configured trusted key +(trust anchor), and never goes to the root name servers to ask for the +DS record for ``.gov``, or ask the root name servers for their DNSKEY. + +In fact, whenever the validating resolver receives a DNSKEY, it checks +to see if this is a configured trusted key to decide whether it +needs to continue chasing down the validation chain. + +.. _trusted_keys_and_managed_keys: + +Trusted Keys and Managed Keys +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Since the resolver is validating, we must have at least one key (trust +anchor) configured. How did it get here, and how do we maintain it? + +If you followed the recommendation in +:ref:`easy_start_guide_for_recursive_servers`, by setting +``dnssec-validation`` to *auto*, there is nothing left to do. +BIND already includes a copy of the root key (in the file +``bind.keys``), and automatically updates it when the root key +changes. [#]_ It looks something like this: + +:: + + trust-anchors { + # This key (20326) was published in the root zone in 2017. + . initial-key 257 3 8 "AwEAAaz/tAm8yTn4Mfeh5eyI96WSVexTBAvkMgJzkKTOiW1vkIbzxeF3 + +/4RgWOq7HrxRixHlFlExOLAJr5emLvN7SWXgnLh4+B5xQlNVz8Og8kv + ArMtNROxVQuCaSnIDdD5LKyWbRd2n9WGe2R8PzgCmr3EgVLrjyBxWezF + 0jLHwVN8efS3rCj/EWgvIWgb9tarpVUDK/b58Da+sqqls3eNbuv7pr+e + oZG+SrDK6nWeL3c6H5Apxz7LjVc1uTIdsIXxuOLYA4/ilBmSVIzuDWfd + RUfhHdY6+cn8HFRm+2hM8AnXGXws9555KrUB5qihylGa8subX2Nn6UwN + R1AkUTV74bU="; + }; + +You can, of course, decide to manage this key manually yourself. +First, you need to make sure that ``dnssec-validation`` is set +to *yes* rather than *auto*: + +:: + + options { + dnssec-validation yes; + }; + +Then, download the root key manually from a trustworthy source, such as +`<https://www.isc.org/bind-keys>`__. Finally, take the root key you +manually downloaded and put it into a ``trust-anchors`` statement as +shown below: + +:: + + trust-anchors { + # This key (20326) was published in the root zone in 2017. + . static-key 257 3 8 "AwEAAaz/tAm8yTn4Mfeh5eyI96WSVexTBAvkMgJzkKTOiW1vkIbzxeF3 + +/4RgWOq7HrxRixHlFlExOLAJr5emLvN7SWXgnLh4+B5xQlNVz8Og8kv + ArMtNROxVQuCaSnIDdD5LKyWbRd2n9WGe2R8PzgCmr3EgVLrjyBxWezF + 0jLHwVN8efS3rCj/EWgvIWgb9tarpVUDK/b58Da+sqqls3eNbuv7pr+e + oZG+SrDK6nWeL3c6H5Apxz7LjVc1uTIdsIXxuOLYA4/ilBmSVIzuDWfd + RUfhHdY6+cn8HFRm+2hM8AnXGXws9555KrUB5qihylGa8subX2Nn6UwN + R1AkUTV74bU="; + }; + +While this ``trust-anchors`` statement and the one in the ``bind.keys`` +file appear similar, the definition of the key in ``bind.keys`` has the +``initial-key`` modifier, whereas in the statement in the configuration +file, that is replaced by ``static-key``. There is an important +difference between the two: a key defined with ``static-key`` is always +trusted until it is deleted from the configuration file. With the +``initial-key`` modified, keys are only trusted once: for as long as it +takes to load the managed key database and start the key maintenance +process. Thereafter, BIND uses the managed keys database +(``managed-keys.bind.jnl``) as the source of key information. + +.. warning:: + + Remember, if you choose to manage the keys on your own, whenever the + key changes (which, for most zones, happens on a periodic basis), + the configuration needs to be updated manually. Failure to do so will + result in breaking nearly all DNS queries for the subdomain of the + key. So if you are manually managing ``.gov``, all domain names in + the ``.gov`` space may become unresolvable; if you are manually + managing the root key, you could break all DNS requests made to your + recursive name server. + +Explicit management of keys was common in the early days of DNSSEC, when +neither the root zone nor many top-level domains were signed. Since +then, `over 90% <https://stats.research.icann.org/dns/tld_report/>`__ of +the top-level domains have been signed, including all the largest ones. +Unless you have a particular need to manage keys yourself, it is best to +use the BIND defaults and let the software manage the root key. + +.. [#] + The root zone was signed in July 2010 and, as at the time of this writing + (mid-2020), the key has been changed once, in October 2018. The intention going + forward is to roll the key once every five years. + +.. _whats_edns0_all_about: + +What's EDNS All About (And Why Should I Care)? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +.. _whats-edns0-all-about-overview: + +EDNS Overview +^^^^^^^^^^^^^ + +Traditional DNS responses are typically small in size (less than 512 +bytes) and fit nicely into a small UDP packet. The Extension mechanism +for DNS (EDNS, or EDNS(0)) offers a mechanism to send DNS data in +larger packets over UDP. To support EDNS, both the DNS server +and the network need to be properly prepared to support the larger +packet sizes and multiple fragments. + +This is important for DNSSEC, since the ``+do`` bit that signals +DNSSEC-awareness is carried within EDNS, and DNSSEC responses are larger +than traditional DNS ones. If DNS servers and the network environment cannot +support large UDP packets, it will cause retransmission over TCP, or the +larger UDP responses will be discarded. Users will likely experience +slow DNS resolution or be unable to resolve certain names at all. + +Note that EDNS applies regardless of whether you are validating DNSSEC, because +BIND has DNSSEC enabled by default. + +Please see :ref:`network_requirements` for more information on what +DNSSEC expects from the network environment. + +.. _edns_on_dns_servers: + +EDNS on DNS Servers +^^^^^^^^^^^^^^^^^^^ + +For many years, BIND has had EDNS enabled by default, +and the UDP packet size is set to a maximum of 4096 bytes. The DNS +administrator should not need to perform any reconfiguration. You can +use ``dig`` to verify that your server supports EDNS and see the UDP packet +size it allows with this ``dig`` command: + +:: + + $ dig @10.53.0.1 www.isc.org. A +dnssec +multiline + + ; <<>> DiG 9.16.0 <<>> @10.53.0.1 ftp.isc.org a +dnssec +multiline + ; (1 server found) + ;; global options: +cmd + ;; Got answer: + ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 48742 + ;; flags: qr rd ra ad; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1 + + ;; OPT PSEUDOSECTION: + ; EDNS: version: 0, flags: do; udp: 4096 + ; COOKIE: 29a9705c2160b08c010000005e67a4a102b9ae079c1b24c8 (good) + ;; QUESTION SECTION: + ;ftp.isc.org. IN A + + ;; ANSWER SECTION: + ftp.isc.org. 300 IN A 149.20.1.49 + ftp.isc.org. 300 IN RRSIG A 13 3 300 ( + 20200401191851 20200302184340 27566 isc.org. + e9Vkb6/6aHMQk/t23Im71ioiDUhB06sncsduoW9+Asl4 + L3TZtpLvZ5+zudTJC2coI4D/D9AXte1cD6FV6iS6PQ== ) + + ;; Query time: 452 msec + ;; SERVER: 10.53.0.1#53(10.53.0.1) + ;; WHEN: Tue Mar 10 14:30:57 GMT 2020 + ;; MSG SIZE rcvd: 187 + +There is a helpful testing tool available (provided by DNS-OARC) that +you can use to verify resolver behavior regarding EDNS support: +`<https://www.dns-oarc.net/oarc/services/replysizetest/>`__ . + +Once you've verified that your name servers have EDNS enabled, that should be the +end of the story, right? Unfortunately, EDNS is a hop-by-hop extension +to DNS. This means the use of EDNS is negotiated between each pair of +hosts in a DNS resolution process, which in turn means if one of your +upstream name servers (for instance, your ISP's recursive name server +that your name server forwards to) does not support EDNS, you may experience DNS +lookup failures or be unable to perform DNSSEC validation. + +.. _support_for_large_packets_network_equipment: + +Support for Large Packets on Network Equipment +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +If both your recursive name server and your ISP's name servers +support EDNS, we are all good here, right? Not so fast. Since these large +packets have to traverse the network, the network infrastructure +itself must allow them to pass. + +When data is physically transmitted over a network, it has to be broken +down into chunks. The size of the data chunk is known as the Maximum +Transmission Unit (MTU), and it can differ from network to +network. IP fragmentation occurs when a large data packet needs to be +broken down into chunks smaller than the +MTU; these smaller chunks then need to be reassembled back into the large +data packet at their destination. IP fragmentation is not necessarily a bad thing, and it most +likely occurs on your network today. + +Some network equipment, such as a firewall, may make assumptions about +DNS traffic. One of these assumptions may be how large each DNS packet +is. When a firewall sees a larger DNS packet than it expects, it may either +reject the large packet or drop its fragments because the firewall +thinks it's an attack. This configuration probably didn't cause problems +in the past, since traditional DNS packets are usually pretty small in +size. However, with DNSSEC, these configurations need to be updated, +since DNSSEC traffic regularly exceeds 1500 bytes (a common MTU value). +If the configuration is not updated to support a larger DNS packet size, +it often results in the larger packets being rejected, and to the +end user it looks like the queries go unanswered. Or in the case of +fragmentation, only a part of the answer makes it to the validating +resolver, and your validating resolver may need to re-ask the question +again and again, creating the appearance for end users that the DNS/network is slow. + +While you are updating the configuration on your network equipment, make +sure TCP port 53 is also allowed for DNS traffic. + +.. _dns_uses_tcp: + +Wait... DNS Uses TCP? +^^^^^^^^^^^^^^^^^^^^^ + +Yes. DNS uses TCP port 53 as a fallback mechanism, when it cannot use +UDP to transmit data. This has always been the case, even long before +the arrival of DNSSEC. Traditional DNS relies on TCP port 53 for +operations such as zone transfer. The use of DNSSEC, or DNS with IPv6 +records such as AAAA, increases the chance that DNS data will be +transmitted via TCP. + +Due to the increased packet size, DNSSEC may fall back to TCP more often +than traditional (insecure) DNS. If your network blocks or +filters TCP port 53 today, you may already experience instability with +DNS resolution, before even deploying DNSSEC. |
