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diff --git a/doc/configuration.rst b/doc/configuration.rst new file mode 100644 index 0000000..922173b --- /dev/null +++ b/doc/configuration.rst @@ -0,0 +1,770 @@ +.. highlight:: none +.. _Configuration: + +************* +Configuration +************* + +Simple configuration +==================== + +The following example presents a simple configuration file +which can be used as a base for your Knot DNS setup:: + + # Example of a very simple Knot DNS configuration. + + server: + listen: 0.0.0.0@53 + listen: ::@53 + + zone: + - domain: example.com + storage: /var/lib/knot/zones/ + file: example.com.zone + + log: + - target: syslog + any: info + +Now let's walk through this configuration step by step: + +- The :ref:`server_listen` statement in the :ref:`server section<Server section>` + defines where the server will listen for incoming connections. + We have defined the server to listen on all available IPv4 and IPv6 addresses, + all on port 53. +- The :ref:`zone section<Zone section>` defines the zones that the server will + serve. In this case, we defined one zone named *example.com* which is stored + in the zone file :file:`/var/lib/knot/zones/example.com.zone`. +- The :ref:`log section<Logging section>` defines the log facilities for + the server. In this example, we told Knot DNS to send its log messages with + the severity ``info`` or more serious to the syslog (or systemd journal). + +For detailed description of all configuration items see +:ref:`Configuration Reference`. + +Zone templates +============== + +A zone template allows a single zone configuration to be shared among several +zones. There is no inheritance between templates; they are exclusive. The +``default`` template identifier is reserved for the default template:: + + template: + - id: default + storage: /var/lib/knot/master + semantic-checks: on + + - id: signed + storage: /var/lib/knot/signed + dnssec-signing: on + semantic-checks: on + master: [master1, master2] + + - id: slave + storage: /var/lib/knot/slave + + zone: + - domain: example1.com # Uses default template + + - domain: example2.com # Uses default template + semantic-checks: off # Override default settings + + - domain: example.cz + template: signed + master: master3 # Override masters to just master3 + + - domain: example1.eu + template: slave + master: master1 + + - domain: example2.eu + template: slave + master: master2 + +.. NOTE:: + Each template option can be explicitly overridden in zone-specific configuration. + +.. _ACL: + +Access control list (ACL) +========================= + +The Access control list is a list of rules specifying remotes which are allowed to +send certain types of requests to the server. +Remotes can be specified by a single IP address or a network subnet. A TSIG +key can also be assigned (see :doc:`keymgr<man_keymgr>` on how to generate a TSIG key). + +Without any ACL rules, all the actions are denied for the zone. Each ACL rule +can allow one or more actions for a given address/subnet/TSIG, or deny them. + +If there are multiple ACL rules for a single zone, they are applied in the order +of appearance in the :ref:`zone_acl` configuration item of a zone or a template. +The first one to match the given remote is applied, the rest is ignored. + +For dynamic updates, additional rules may be specified, which will allow or deny updates +according to the type or owner of Resource Records in the update. + +See the following examples and :ref:`ACL section`. + +:: + + acl: + - id: address_rule + address: [2001:db8::1, 192.168.2.0/24] + action: transfer + + - id: deny_rule + address: 192.168.2.100 + action: transfer + deny: on + + zone: + - domain: acl1.example.com. + acl: [deny_rule, address_rule] # deny_rule first here to take precendence + +:: + + key: + - id: key1 # The real TSIG key name + algorithm: hmac-md5 + secret: Wg== + + acl: + - id: deny_all + address: 192.168.3.0/24 + deny: on # no action specified and deny on implies denial of all actions + + - id: key_rule + key: key1 # Access based just on TSIG key + action: [transfer, notify] + + zone: + - domain: acl2.example.com + acl: [deny_all, key_rule] + +:: + + acl + - id: owner_type_rule + action: update + update-type: [A, AAAA, MX] # Updates are only allowed to update records of the specified types + update-owner: name # The allowed owners are specified by the list on the next line + update-owner-name: [a, b.example.com.] # Non-FQDN names are relative to the effective zone name + update-owner-match: equal # The owners of records in an update must be exactly equal to the names in the list + +.. NOTE:: + If more conditions (address ranges and/or a key) + are given in a single ACL rule, all of them have to be satisfied for the rule to match. + +.. TIP:: + In order to restrict regular DNS queries, use module :ref:`queryacl<mod-queryacl>`. + +Secondary (slave) zone +====================== + +Knot DNS doesn't strictly differ between primary (formerly known as master) +and secondary (formerly known as slave) zones. The only requirement for a secondary +zone is to have a :ref:`zone_master` statement set. Also note that you need +to explicitly allow incoming zone changed notifications via ``notify`` :ref:`acl_action` +through a zone's :ref:`zone_acl` list, otherwise the update will be rejected by the +server. If the zone file doesn't exist it will be bootstrapped over AXFR:: + + remote: + - id: master + address: 192.168.1.1@53 + + acl: + - id: notify_from_master + address: 192.168.1.1 + action: notify + + zone: + - domain: example.com + storage: /var/lib/knot/zones/ + # file: example.com.zone # Default value + master: master + acl: notify_from_master + +Note that the :ref:`zone_master` option accepts a list of multiple remotes. +The remotes should be listed according to their preference. The first remote +has the highest preference, the other remotes are used for failover. When the +server receives a zone update notification from a listed remote, that remote +will be the most preferred one for the subsequent transfer. + +To use TSIG for transfers and notification messages authentication, configure +a TSIG key and assign the key both to the remote and the ACL rule. Notice that +the :ref:`remote <Remote section>` and :ref:`ACL <ACL section>` definitions are +independent:: + + key: + - id: slave1_key + algorithm: hmac-md5 + secret: Wg== + + remote: + - id: master + address: 192.168.1.1@53 + key: slave1_key + + acl: + - id: notify_from_master + address: 192.168.1.1 + key: slave1_key + action: notify + +.. NOTE:: + When transferring a lot of zones, the server may easily get into a state + where all available ports are in the TIME_WAIT state, thus transfers + cease until the operating system closes the ports for good. There are + several ways to work around this: + + * Allow reusing of ports in TIME_WAIT (sysctl -w net.ipv4.tcp_tw_reuse=1) + * Shorten TIME_WAIT timeout (tcp_fin_timeout) + * Increase available local port count + +Primary (master) zone +===================== + +An ACL with the ``transfer`` action must be configured to allow outgoing zone +transfers. An ACL rule consists of a single address or a network subnet:: + + remote: + - id: slave1 + address: 192.168.2.1@53 + + acl: + - id: slave1_acl + address: 192.168.2.1 + action: transfer + + - id: others_acl + address: 192.168.3.0/24 + action: transfer + + zone: + - domain: example.com + storage: /var/lib/knot/zones/ + file: example.com.zone + notify: slave1 + acl: [slave1_acl, others_acl] + +Optionally, a TSIG key can be specified:: + + key: + - id: slave1_key + algorithm: hmac-md5 + secret: Wg== + + remote: + - id: slave1 + address: 192.168.2.1@53 + key: slave1_key + + acl: + - id: slave1_acl + address: 192.168.2.1 + key: slave1_key + action: transfer + + - id: others_acl + address: 192.168.3.0/24 + action: transfer + +Note that a secondary zone may serve as a primary zone at the same time:: + + remote: + - id: master + address: 192.168.1.1@53 + - id: slave1 + address: 192.168.2.1@53 + + acl: + - id: notify_from_master + address: 192.168.1.1 + action: notify + + - id: slave1_acl + address: 192.168.2.1 + action: transfer + + - id: others_acl + address: 192.168.3.0/24 + action: transfer + + zone: + - domain: example.com + storage: /var/lib/knot/zones/ + file: example.com.zone + master: master + notify: slave1 + acl: [notify_from_master, slave1_acl, others_acl] + +Dynamic updates +=============== + +Dynamic updates for the zone are allowed via proper ACL rule with the +``update`` action. If the zone is configured as a secondary and a DNS update +message is accepted, the server forwards the message to its primary master. +The primary master's response is then forwarded back to the originator. + +However, if the zone is configured as a primary, the update is accepted and +processed:: + + acl: + - id: update_acl + address: 192.168.3.0/24 + action: update + + zone: + - domain: example.com + file: example.com.zone + acl: update_acl + +.. _dnssec: + +Automatic DNSSEC signing +======================== + +Knot DNS supports automatic DNSSEC signing for static zones. The signing +can operate in two modes: + +1. :ref:`Automatic key management <dnssec-automatic-zsk-management>`. + In this mode, the server maintains signing keys. New keys are generated + according to assigned policy and are rolled automatically in a safe manner. + No zone operator intervention is necessary. + +2. :ref:`Manual key management <dnssec-manual-key-management>`. + In this mode, the server maintains zone signatures only. The signatures + are kept up-to-date and signing keys are rolled according to timing + parameters assigned to the keys. The keys must be generated and timing + parameters must be assigned by the zone operator. + +The DNSSEC signing process maintains some metadata which is stored in the +:abbr:`KASP (Key And Signature Policy)` database. This database is backed +by LMDB. + +.. WARNING:: + Make sure to set the KASP database permissions correctly. For manual key + management, the database must be *readable* by the server process. For + automatic key management, it must be *writeable*. If no HSM is used, + the database also contains private key material – don't set the permissions + too weak. + +.. _dnssec-automatic-zsk-management: + +Automatic ZSK management +------------------------ + +For automatic ZSK management a signing :ref:`policy<Policy section>` has to +be configured and assigned to the zone. The policy specifies how the zone +is signed (i.e. signing algorithm, key size, key lifetime, signature lifetime, +etc.). If no policy is specified or the ``default`` one is assigned, the +default signing parameters are used. + +A minimal zone configuration may look as follows:: + + zone: + - domain: myzone.test + dnssec-signing: on + +With a custom signing policy, the policy section will be added:: + + policy: + - id: rsa + algorithm: RSASHA256 + ksk-size: 2048 + zsk-size: 1024 + + zone: + - domain: myzone.test + dnssec-signing: on + dnssec-policy: rsa + +After configuring the server, reload the changes: + +.. code-block:: console + + $ knotc reload + +The server will generate initial signing keys and sign the zone properly. Check +the server logs to see whether everything went well. + +.. WARNING:: + This guide assumes that the zone *myzone.test* was not signed prior to + enabling the automatic key management. If the zone was already signed, all + existing keys must be imported using ``keymgr import-bind`` command + before enabling the automatic signing. Also the algorithm in the policy must + match the algorithm of all imported keys. Otherwise the zone will be completely + re-signed with a new, automatically generated key. + +.. _dnssec-automatic-ksk-management: + +Automatic KSK management +------------------------ + +For automatic KSK management, first configure ZSK management like above, and use +additional options in :ref:`policy section <Policy section>`, mostly specifying +desired (finite) lifetime for KSK: :: + + remote: + - id: parent_zone_server + address: 192.168.12.1@53 + + submission: + - id: parent_zone_sbm + parent: [parent_zone_server] + + policy: + - id: rsa + algorithm: RSASHA256 + ksk-size: 2048 + zsk-size: 1024 + zsk-lifetime: 30d + ksk-lifetime: 365d + ksk-submission: parent_zone_sbm + + zone: + - domain: myzone.test + dnssec-signing: on + dnssec-policy: rsa + +After the initially-generated KSK reaches its lifetime, new KSK is published and after +convenience delay the submission is started. The server publishes CDS and CDNSKEY records +and the user shall propagate them to the parent. The server periodically checks for +DS at the parent zone and when positive, finishes the rollover. + +To share KSKs among zones, set the ksk-shared policy parameter. It is strongly discouraged to +change the policy ``id`` afterwards! The shared key's creation timestamp will be equal for all +zones, but other timers (e.g. activate, retire) may get out of sync. :: + + policy: + - id: shared + ... + ksk-shared: true + + zone: + - domain: firstzone.test + dnssec-signing: on + dnssec-policy: shared + + zone: + - domain: secondzone.test + dnssec-signing: on + dnssec-policy: shared + +.. _dnssec-manual-key-management: + +Manual key management +--------------------- + +For automatic DNSSEC signing with manual key management, a signing policy +with manual key management flag has to be set:: + + policy: + - id: manual + manual: on + + zone: + - domain: myzone.test + dnssec-signing: on + dnssec-policy: manual + +To generate signing keys, use the :doc:`keymgr<man_keymgr>` utility. +For example, we can use Single-Type Signing: + +.. code-block:: console + + $ keymgr myzone.test. generate algorithm=ECDSAP256SHA256 ksk=yes zsk=yes + +And reload the server. The zone will be signed. + +To perform a manual rollover of a key, the timing parameters of the key need +to be set. Let's roll the key. Generate a new key, but do not activate +it yet: + +.. code-block:: console + + $ keymgr myzone.test. generate algorithm=ECDSAP256SHA256 ksk=yes zsk=yes active=+1d + +Take the key ID (or key tag) of the old key and disable it the same time +the new key gets activated: + +.. code-block:: console + + $ keymgr myzone.test. set <old_key_id> retire=+2d remove=+3d + +Reload the server again. The new key will be published (i.e. the DNSKEY record +will be added into the zone). Remember to update the DS record in the +parent zone to include a reference to the new key. This must happen within one +day (in this case) including a delay required to propagate the new DS to +caches. + +.. WARNING:: + If you ever decide to switch from manual key management to automatic key management, + note that the automatic key management uses + :ref:`policy_zsk-lifetime` and :ref:`policy_ksk-lifetime` policy configuration + options to schedule key rollovers and it internally uses timestamps of keys differently + than in the manual case. As a consequence it might break if the ``retire`` or ``remove`` timestamps + are set for the manually generated keys currently in use. Make sure to set these timestamps + to zero using :doc:`keymgr<man_keymgr>`: + + .. code-block:: console + + $ keymgr myzone.test. set <key_id> retire=0 remove=0 + + and configure your policy suitably according to :ref:`dnssec-automatic-zsk-management` + and :ref:`dnssec-automatic-ksk-management`. + +.. _dnssec-signing: + +Zone signing +------------ + +The signing process consists of the following steps: + +#. Processing KASP database events. (e.g. performing a step of a rollover). +#. Updating the DNSKEY records. The whole DNSKEY set in zone apex is replaced + by the keys from the KASP database. Note that keys added into the zone file + manually will be removed. To add an extra DNSKEY record into the set, the + key must be imported into the KASP database (possibly deactivated). +#. Fixing the NSEC or NSEC3 chain. +#. Removing expired signatures, invalid signatures, signatures expiring + in a short time, and signatures issued by an unknown key. +#. Creating missing signatures. Unless the Single-Type Signing Scheme + is used, DNSKEY records in a zone apex are signed by KSK keys and + all other records are signed by ZSK keys. +#. Updating and re-signing SOA record. + +The signing is initiated on the following occasions: + +- Start of the server +- Zone reload +- Reaching the signature refresh period +- Key set changed due to rollover event +- Received DDNS update +- Forced zone re-sign via server control interface + +On a forced zone re-sign, all signatures in the zone are dropped and recreated. + +The ``knotc zone-status`` command can be used to see when the next scheduled +DNSSEC re-sign will happen. + +.. _dnssec-on-slave-signing: + +On-secondary (on-slave) signing +------------------------------- + +It is possible to enable automatic DNSSEC zone signing even on a secondary +server. If enabled, the zone is signed after every AXFR/IXFR transfer +from primary, so that the secondary always serves a signed up-to-date version +of the zone. + +It is strongly recommended to block any outside access to the primary +server, so that only the secondary server's signed version of the zone is served. + +Enabled on-secondary signing introduces events when the secondary zone changes +while the primary zone remains unchanged, such as a key rollover or +refreshing of RRSIG records, which cause inequality of zone SOA serial +between primary and secondary. The secondary server handles this by saving the +primary's SOA serial in a special variable inside KASP DB and appropriately +modifying AXFR/IXFR queries/answers to keep the communication with +primary server consistent while applying the changes with a different serial. + +.. _catalog-zones: + +Catalog zones +============= + +Catalog zones are a concept whereby a list of zones to be configured is maintained +as contents of a separate, special zone. This approach has the benefit of simple +propagation of a zone list to secondary servers, especially when the list is +frequently updated. Currently, catalog zones are described in this `Internet Draft +<https://tools.ietf.org/html/draft-ietf-dnsop-dns-catalog-zones>`_. + +Terminology first. *Catalog zone* is a meta-zone which shall not be a part +of the DNS tree, but it contains information about the set of member zones and +is transferable to secondary servers using common AXFR/IXFR techniques. +*Catalog-member zone* (or just *member zone*) is a zone based on +information from the catalog zone and not from configuration file/database. + +A catalog zone is handled almost in the same way as a regular zone: +It can be configured using all the standard options (but for example +DNSSEC signing would be useless), including primary/secondary configuration +and ACLs. A catalog zone is indicated by setting the option +:ref:`zone_catalog-role`. The difference is that standard DNS +queries to a catalog zone are answered with REFUSED as though the zone +doesn't exist, unless querying over TCP from an address with transfers enabled +by ACL. The name of the catalog zone is arbitrary. It's required to +include version record ``version 0 IN TXT "2"``, however. +It's possible to configure multiple catalog zones. + +.. WARNING:: + Don't choose a name for a catalog zone below a name of any other + existing zones configured on the server as it would effectively "shadow" + part of your DNS subtree. + +Upon catalog zone (re)load or change, all the PTR records in the zone +sub-tree *zones* (e.g. ``unique-id1.zones.catalog. 0 IN PTR member.com.``) +are processed and member zones created, with zone names taken from the +PTR records' RData, and zone settings taken from the configuration +template specified by :ref:`zone_catalog-template`. Owner names of those PTR +records may be arbitrary, but when a member zone is de-cataloged and +re-cataloged again, the owner name of the relevant PTR record must +be changed. It's also recommended that all the PTR records have different +owner names (in other words, catalog zone RRSets consist of one RR each) +to prevent oversized RRSets (not AXFR-able) and to achieve interoperability. + +All records other than PTR are ignored. They remain in the catalog +zone, however, and might be for example transferred to a secondary server, which may interpret +catalog zones differently. SOA still needs to be present in the catalog zone +and its serial handled appropriately. An apex NS record should be present +for the sake of interoperability. + +A catalog zone may be modified using any standard means (e.g. AXFR/IXFR, DDNS, +zone file reload). In the case of incremental change, only affected +member zones are reloaded. + +Any de-cataloged member zone is purged immediately, including its +zone file, journal, timers, and DNSSEC keys. The zone file is not +deleted if :ref:`zone_zonefile-sync` is set to *-1* for member zones. + +When setting up catalog zones, it might be useful to set +:ref:`database_catalog-db` and :ref:`database_catalog-db-max-size` +to non-default values. + +.. WARNING:: + Bugs, limitations: + + Knot does purge the member zone's metadata whenever the respective PTR + record owner changes in any way. This differs from the specification + (see `Internet Draft` above), + which requires this to be done only when the "unique" label (i.e. the + one immediately left of the `zones` label) changes. It's expected that + Knot's behaviour will be aligned to the specification in the future. + + Knot does not work well if one member zone appears in two catalog zones + concurrently. The user is encouraged to avoid this situation whatsoever. + Thus, there is no way a member zone can be migrated from one catalog + to another while preserving its metadata. Following steps may be used + as a workaround: + + * :ref:`Back up<Data and metadata backup>` the member zone's metadata + (on each server separately). + * Remove the member zone from the catalog it's a member of. + * Wait for the catalog zone to be propagated to all servers. + * Add the member zone to the other catalog. + * Restore the backed up metadata (on each server separately). + +.. _query-modules: + +Query modules +============= + +Knot DNS supports configurable query modules that can alter the way +queries are processed. Each query requires a finite number of steps to +be resolved. We call this set of steps a *query plan*, an abstraction +that groups these steps into several stages. + +* Before-query processing +* Answer, Authority, Additional records packet sections processing +* After-query processing + +For example, processing an Internet-class query needs to find an +answer. Then based on the previous state, it may also append an +authority SOA or provide additional records. Each of these actions +represents a 'processing step'. Now, if a query module is loaded for a +zone, it is provided with an implicit query plan which can be extended +by the module or even changed altogether. + +A module is active if its name, which includes the ``mod-`` prefix, is assigned +to the zone/template :ref:`zone_module` option or to the ``default`` template +:ref:`template_global-module` option if activating for all queries. +If the module is configurable, a corresponding module section with +an identifier must be created and then referenced in the form of +``module_name/module_id``. See :ref:`Modules` for the list of available modules. + +.. NOTE:: + Query modules are processed in the order they are specified in the + zone/template configuration. In most cases, the recommended order is:: + + mod-synthrecord, mod-onlinesign, mod-cookies, mod-rrl, mod-dnstap, mod-stats + +Performance Tuning +================== + +Numbers of Workers +------------------ + +There are three types of workers ready for parallel execution of performance-oriented tasks: +UDP workers, TCP workers, and Background workers. The first two types handle all network requests +via the UDP and TCP protocol (respectively) and do the response jobs for common +queries. Background workers process changes to the zone. + +By default, Knot determines a well-fitting number of workers based on the number of CPU cores. +The user can specify the number of workers for each type with configuration/server section: +:ref:`server_udp-workers`, :ref:`server_tcp-workers`, :ref:`server_background-workers`. + +An indication of when to increase the number of workers is when the server is lagging behind +expected performance, while CPU usage remains low. This is usually due to waiting for network +or I/O response during the operation. It may be caused by Knot design not fitting the use-case well. +The user should try increasing the number of workers (of the related type) slightly above 100 and if +the performance improves, decide a further, exact setting. + +Number of available file descriptors +------------------------------------ + +A name server configured for a large number of zones (hundreds or more) needs enough file descriptors +available for zone transfers and zone file updates, which default OS settings often don't provide. +It's necessary to check with the OS configuration and documentation and ensure the number of file +descriptors (sometimes called a number of concurrently open files) effective for the knotd process +is set suitably high. The number of concurrently open incoming TCP connections must be taken into +account too. In other words, the required setting is affected by the :ref:`server_tcp-max-clients` +setting. + +Sysctl and NIC optimizations +---------------------------- + +There are several recommendations based on Knot developers' experience with their specific HW and SW +(mainstream Intel-based servers, Debian-based GNU/Linux distribution). They may improve or impact +performance in common use cases. + +If your NIC driver allows it (see /proc/interrupts for hint), set CPU affinity (/proc/irq/$IRQ/smp_affinity) +manually so that each NIC channel is served by unique CPU core(s). You must turn off irqbalance service +in advance to avoid configuration override. + +Configure sysctl as follows: :: + + socket_bufsize=1048576 + busy_latency=0 + backlog=40000 + optmem_max=20480 + + net.core.wmem_max = $socket_bufsize + net.core.wmem_default = $socket_bufsize + net.core.rmem_max = $socket_bufsize + net.core.rmem_default = $socket_bufsize + net.core.busy_read = $busy_latency + net.core.busy_poll = $busy_latency + net.core.netdev_max_backlog = $backlog + net.core.optmem_max = $optmem_max + +Disable huge pages. + +Configure your CPU to "performance" mode. This can be achieved depending on architecture, e.g. in BIOS, +or e.g. configuring /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor to "performance". + +Tune your NIC device with ethtool: :: + + ethtool -A $dev autoneg off rx off tx off + ethtool -K $dev tso off gro off ufo off + ethtool -G $dev rx 4096 tx 4096 + ethtool -C $dev rx-usecs 75 + ethtool -C $dev tx-usecs 75 + ethtool -N $dev rx-flow-hash udp4 sdfn + ethtool -N $dev rx-flow-hash udp6 sdfn + +On FreeBSD you can just: :: + + ifconfig ${dev} -rxcsum -txcsum -lro -tso + +Knot developers are open to hear about users' further suggestions about network devices tuning/optimization. |