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diff --git a/doc/operation.rst b/doc/operation.rst new file mode 100644 index 0000000..d27642d --- /dev/null +++ b/doc/operation.rst @@ -0,0 +1,1200 @@ +.. highlight:: console +.. _Operation: + +********* +Operation +********* + +The Knot DNS server part :doc:`knotd<man_knotd>` can run either in the foreground, +or in the background using the ``-d`` option. When run in the foreground, it +doesn't create a PID file. Other than that, there are no differences and you +can control both the same way. + +The tool :doc:`knotc<man_knotc>` is designed as a user front-end, making it easier +to control a running server daemon. If you want to control the daemon directly, +use ``SIGINT`` to quit the process or ``SIGHUP`` to reload the configuration. + +If you pass neither configuration file (``-c`` parameter) nor configuration +database (``-C`` parameter), the server will first attempt to use the default +configuration database stored in ``/var/lib/knot/confdb`` or the +default configuration file stored in ``/etc/knot/knot.conf``. Both the +default paths can be reconfigured with ``--with-storage=path`` or +``--with-configdir=path`` respectively. + +Example of server start as a daemon:: + + $ knotd -d -c knot.conf + +Example of server shutdown:: + + $ knotc -c knot.conf stop + +For a complete list of actions refer to the program help (``-h`` parameter) +or to the corresponding manual page. + +Also, the server needs to create :ref:`server_rundir` and :ref:`zone_storage` +directories in order to run properly. + +.. _Configuration database: + +Configuration database +====================== + +In the case of a huge configuration file, the configuration can be stored +in a binary database. Such a database can be simply initialized:: + + $ knotc conf-init + +or preloaded from a file:: + + $ knotc conf-import input.conf + +Also the configuration database can be exported into a textual file:: + + $ knotc conf-export output.conf + +.. WARNING:: + The import and export commands access the configuration database + directly, without any interaction with the server. Therefore, any data + not yet committed to the database won't be exported. And the server won't + reflect imported configuration correctly. So it is strictly recommended to + import new configuration when the server is not running. + +.. _Dynamic configuration: + +Dynamic configuration +===================== + +The configuration database can be accessed using the server control interface +while the server is running. To get the full power of the dynamic configuration, +the server must be started with a specified configuration database location +or with the default database initialized. Otherwise all the changes to the +configuration will be temporary (until the server is stopped). + +.. NOTE:: + The database can be :ref:`imported<Configuration database>` in advance. + +Most of the commands get an item name and value parameters. The item name is +in the form of ``section[identifier].name``. If the item is multivalued, +more values can be specified as individual (command line) arguments. + +.. CAUTION:: + Beware of the possibility of pathname expansion by the shell. For this reason, + it is advisable to escape (with backslash) square brackets or to quote command parameters if + not executed in the interactive mode. + +To get the list of configuration sections or to get the list of section items:: + + $ knotc conf-list + $ knotc conf-list 'server' + +To get the whole configuration or to get the whole configuration section or +to get all section identifiers or to get a specific configuration item:: + + $ knotc conf-read + $ knotc conf-read 'remote' + $ knotc conf-read 'zone.domain' + $ knotc conf-read 'zone[example.com].master' + +.. WARNING:: + The following operations don't work on OpenBSD! + +Modifying operations require an active configuration database transaction. +Just one transaction can be active at a time. Such a transaction then can +be aborted or committed. A semantic check is executed automatically before +every commit:: + + $ knotc conf-begin + $ knotc conf-abort + $ knotc conf-commit + +To set a configuration item value or to add more values or to add a new +section identifier or to add a value to all identified sections:: + + $ knotc conf-set 'server.identity' 'Knot DNS' + $ knotc conf-set 'server.listen' '0.0.0.0@53' '::@53' + $ knotc conf-set 'zone[example.com]' + $ knotc conf-set 'zone.slave' 'slave2' + +.. NOTE:: + Also the include operation can be performed. A non-absolute file + location is relative to the server binary path, not to the control binary + path! + + :: + + $ knotc conf-set 'include' '/tmp/new_zones.conf' + +To unset the whole configuration or to unset the whole configuration section +or to unset an identified section or to unset an item or to unset a specific +item value:: + + $ knotc conf-unset + $ knotc conf-unset 'zone' + $ knotc conf-unset 'zone[example.com]' + $ knotc conf-unset 'zone[example.com].master' + $ knotc conf-unset 'zone[example.com].master' 'remote2' 'remote5' + +To get the change between the current configuration and the active transaction +for the whole configuration or for a specific section or for a specific +identified section or for a specific item:: + + $ knotc conf-diff + $ knotc conf-diff 'zone' + $ knotc conf-diff 'zone[example.com]' + $ knotc conf-diff 'zone[example.com].master' + +.. CAUTION:: + While it is possible to change most of the configuration parameters + dynamically or via configuration file reload, a few of the parameters + in the section ``server`` require restarting the server, such that the changes + take effect. These parameters are: + :ref:`rundir<server_rundir>`, + :ref:`user<server_user>`, + :ref:`pidfile<server_pidfile>`, + :ref:`tcp-reuseport<server_tcp-reuseport>`, + :ref:`udp-workers<server_udp-workers>`, + :ref:`tcp-workers<server_tcp-workers>`, + :ref:`background-workers<server_background-workers>`, and + :ref:`listen<server_listen>`. + +An example of possible configuration initialization:: + + $ knotc conf-begin + $ knotc conf-set 'server.listen' '0.0.0.0@53' '::@53' + $ knotc conf-set 'remote[master_server]' + $ knotc conf-set 'remote[master_server].address' '192.168.1.1' + $ knotc conf-set 'template[default]' + $ knotc conf-set 'template[default].storage' '/var/lib/knot/zones/' + $ knotc conf-set 'template[default].master' 'master_server' + $ knotc conf-set 'zone[example.com]' + $ knotc conf-diff + $ knotc conf-commit + +.. _Secondary mode: + +Secondary (slave) mode +====================== + +Running the server as a secondary is very straightforward as the zone +is transfered automatically from a remote server. The received zone is +usually stored in a zone file after the :ref:`zone_zonefile-sync` period +elapses. Zone differences are stored in the :ref:`zone journal <Journal behaviour>`. + +.. _Primary mode: + +Primary (master) mode +===================== + +If you just want to check the zone files before starting, you can use:: + + $ knotc zone-check example.com + +.. _Editing zones: + +Reading and editing zones +========================= + +Knot DNS allows you to read or change zone contents online using the server +control interface. + +.. WARNING:: + Avoid concurrent zone access when a zone event (zone file load, refresh, + DNSSEC signing, dynamic update) is in progress or pending. In such a case + zone events must be frozen before. For more information on how to freeze the + zone read :ref:`Editing zone file`. + +To get contents of all configured zones, or a specific zone contents, or zone +records with a specific owner, or even with a specific record type:: + + $ knotc zone-read -- + $ knotc zone-read example.com + $ knotc zone-read example.com ns1 + $ knotc zone-read example.com ns1 NS + +.. NOTE:: + If the record owner is not a fully qualified domain name, then it is + considered as a relative name to the zone name. + +To start a writing transaction on all zones or on specific zones:: + + $ knotc zone-begin -- + $ knotc zone-begin example.com example.net + +Now you can list all nodes within the transaction using the ```zone-get``` +command, which always returns current data with all changes included. The +command has the same syntax as ```zone-read```. + +Within the transaction, you can add a record to a specific zone or to all +zones with an open transaction:: + + $ knotc zone-set example.com ns1 3600 A 192.168.0.1 + $ knotc zone-set -- ns1 3600 A 192.168.0.1 + +To remove all records with a specific owner, or a specific rrset, or +specific record data:: + + $ knotc zone-unset example.com ns1 + $ knotc zone-unset example.com ns1 A + $ knotc zone-unset example.com ns1 A 192.168.0.2 + +To see the difference between the original zone and the current version:: + + $ knotc zone-diff example.com + +Finally, either commit or abort your transaction:: + + $ knotc zone-commit example.com + $ knotc zone-abort example.com + +A full example of setting up a completely new zone from scratch:: + + $ knotc conf-begin + $ knotc conf-set zone.domain example.com + $ knotc conf-commit + $ knotc zone-begin example.com + $ knotc zone-set example.com @ 7200 SOA ns hostmaster 1 86400 900 691200 3600 + $ knotc zone-set example.com ns 3600 A 192.168.0.1 + $ knotc zone-set example.com www 3600 A 192.168.0.100 + $ knotc zone-commit example.com + +.. NOTE:: + If quotes are necessary for record data specification, remember to escape them:: + + $ knotc zone-set example.com @ 3600 TXT \"v=spf1 a:mail.example.com -all\" + +.. _Editing zone file: + +Reading and editing the zone file safely +======================================== + +It's always possible to read and edit zone contents via zone file manipulation. +It may lead to confusion, however, if the zone contents are continuously being +changed by DDNS, DNSSEC signing and the like. In such a case, the safe way to +modify the zone file is to freeze zone events first:: + + $ knotc -b zone-freeze example.com. + $ knotc -b zone-flush example.com. + +After calling freeze on the zone, there still may be running zone operations (e.g. signing), +causing freeze pending. Because of this, the blocking mode is used to ensure +the operation was finished. Then the zone can be flushed to a file. + +Now the zone file can be safely modified (e.g. using a text editor). +If :ref:`zone_zonefile-load` is not set to `difference-no-serial`, it's also necessary to +**increase SOA serial** in this step to keep consistency. Finally, we can load the +modified zone file and if successful, thaw the zone:: + + $ knotc -b zone-reload example.com. + $ knotc zone-thaw example.com. + +.. _Zone loading: + +Zone loading +============ + +The process of how the server loads a zone is influenced by the configuration of the +:ref:`zonefile-load <zone_zonefile-load>` and :ref:`journal-content <zone_journal-content>` +parameters (also DNSSEC signing applies), the existence of a zone file and journal +(and their relative out-of-dateness), and whether it is a cold start of the server +or a zone reload (e.g. invoked by the :doc:`knotc<man_knotc>` interface). Please note +that zone transfers are not taken into account here – they are planned after the zone +is loaded (including :ref:`zone bootstrap<Zone bootstrap>`). + +If the zone file exists and is not excluded by the configuration, it is first loaded +and according to its SOA serial number, relevant journal changesets are applied. +If this is a zone reload and we have :ref:`zone_zonefile-load` set to `difference`, the difference +between old and new contents is computed and stored in the journal like an update. +The zone file should be either unchanged since last load or changed with incremented +SOA serial. In the case of a decreased SOA serial, the load is interrupted with +an error; if unchanged, it is increased by the server. + +If the procedure described above succeeds without errors, the resulting zone contents are (after potential DNSSEC signing) +used as the new zone. + +The option :ref:`zone_journal-content` set to `all` lets the server, beside better performance, keep +track of the zone contents also across server restarts. It makes the cold start +effectively work like a zone reload with the old contents loaded from the journal +(unless this is the very first start with the zone not yet saved into the journal). + +.. _Journal behaviour: + +Journal behaviour +================= + +The zone journal keeps some history of changes made to the zone. It is useful for +responding to IXFR queries. Also if :ref:`zone file flush <zone_zonefile-sync>` is disabled, the +journal keeps the difference between the zone file and the current zone in case of server shutdown. +The history is stored in changesets – differences of zone contents between two +(usually subsequent) zone versions (specified by SOA serials). + +Journals of all zones are stored in a common LMDB database. Huge changesets are +split into 70 KiB [#fn-hc]_ blocks to prevent fragmentation of the DB. The +journal does each operation in one transaction to keep consistency of the DB and performance. + +Each zone journal has its own occupation limits :ref:`maximum usage <zone_journal-max-usage>` +and :ref:`maximum depth <zone_journal-max-depth>`. Changesets are stored in the journal +one by one. When hitting any of the limits, the zone is flushed into the zone file +if there are no redundant changesets to delete, and the oldest changesets are deleted. +In the case of the size limit, twice [#fn-hc]_ the needed amount of space is purged +to prevent overly frequent deletes. + +If :ref:`zone file flush <zone_zonefile-sync>` is disabled, then instead of flushing +the zone, the journal tries to save space by merging the changesets into a special one. +This approach is effective if the changes rewrite each other, e.g. periodically +changing the same zone records, re-signing the whole zone etc. Thus the difference between the zone +file and the zone is still preserved even if the journal deletes some older changesets. + +If the journal is used to store both zone history and contents, a special changeset +is present with zone contents. When the journal gets full, the changes are merged into this +special changeset. + +There is also a :ref:`safety hard limit <database_journal-db-max-size>` for overall +journal database size, but it's strongly recommended to set the per-zone limits in +a way to prevent hitting this one. For LMDB, it's hard to recover from the +database-full state. For wiping one zone's journal, see *knotc zone-purge +journal* +command. + +.. [#fn-hc] This constant is hardcoded. + +.. _Handling, zone file, journal, changes, serials: + +Handling zone file, journal, changes, serials +============================================= + +Some configuration options regarding the zone file and journal, together with operation +procedures, might lead to unexpected results. This chapter points out +potential interference and both recommends and warns before some combinations thereof. +Unfortunately, there is no optimal combination of configuration options, +every approach has some disadvantages. + +Example 1 +--------- + +Keep the zone file updated:: + + zonefile-sync: 0 + zonefile-load: whole + journal-content: changes + +These are default values. The user can always check the current zone +contents in the zone file, and also modify it (recommended with server turned-off or +taking the :ref:`safe way<Editing zone file>`). The journal serves here just as a source of +history for secondary servers' IXFR. Some users dislike that the server overwrites their +prettily prepared zone file. + +Example 2 +--------- + +Zonefileless setup:: + + zonefile-sync: -1 + zonefile-load: none + journal-content: all + +Zone contents are stored only in the journal. The zone is updated by DDNS, +zone transfer, or via the control interface. The user might have filled the +zone contents initially from a zone file by setting :ref:`zone_zonefile-load` to +`whole` temporarily. +It's also a good setup for secondary servers. Anyway, it's recommended to carefully tune +the journal-size-related options to avoid surprises like the journal getting full. + +Example 3 +--------- + +Input-only zone file:: + + zonefile-sync: -1 + zonefile-load: difference + journal-content: changes + +The user can make changes to the zone by editing the zone file, and his pretty zone file +is never overwritten or filled with DNSSEC-related autogenerated records – they are +only stored in the journal. + +The zone file's SOA serial must be properly set to a number which is higher than the +current SOA serial in the zone (not in the zone file) if manually updated! + +Example 4 +--------- + +Auto-increment SOA serial:: + + zonefile-sync: -1 + zonefile-load: difference-no-serial + journal-content: all + +This is similar to the previous setup, but the SOA serial is handled by the server +automatically. So the user no longer needs to care about it in the zone file. + +However, this requires setting :ref:`zone_journal-content` to `all` so that +the information about the last real SOA serial is preserved in case of server re-start. + +.. _Zone bootstrap: + +Zone bootstrapping on secondary +=============================== + +When zone refresh from the primary fails, the ``retry`` value from SOA is used +as the interval between refresh attempts. In a case that SOA isn't known to the +secondary (either because the zone hasn't been retrieved from the primary yet, +or the zone has expired), a backoff is used for repeated retry attempts. + +With every retry, the delay rises as a quadratic polynomial (5 * n^2, where n +represents the sequence number of the retry attempt) up to two hours, each time +with a random delay of 0 to 30 seconds added to spread the load on the primary. +In each attempt, the retry interval is subject to :ref:`zone_retry-min-interval` +and :ref:`zone_retry-max-interval`. + +Until the refresh has been successfully completed, the backoff is restarted from +the beginning by every ```zone-refresh``` or ```zone-retransfer``` of the zone +triggered manually via :doc:`knotc<man_knotc>`, by ```zone-purge``` or +```zone-restore``` of the zone's timers, or by a restart of :doc:`knotd<man_knotd>`. + +.. _Zone expiration: + +Zone expiration +=============== + +On a primary, zone normally never expires. On a secondary, zone expiration results +in removal of the current zone contents and a trigger of immediate zone refresh. +The zone file and zone's journal are kept, but not used for answering requests +until the refresh is successfully completed. + +The zone expire timer is set according to the zone's SOA expire field. In addition +to it, Knot DNS also supports EDNS EXPIRE extension of the expire timer in both +primary and secondary roles as described in :rfc:`7314`. + +When Knot DNS is configured as a secondary, EDNS EXPIRE option present in a SOA, +IXFR, or AFXR response from the primary is processed and used to update the zone +timer when necessary. This functionality (together with requests of any other EDNS +options) for a specified primary may be disabled using the :ref:`remote_no-edns` +configuration parameter. + +If it's necessary, any zone may be expired manually using the ``zone-purge`` +command of the :doc:`knotc<man_knotc>` utility. Manual expiration is applicable +to any zone, including a catalog zone or a zone on a primary. Beware, a manually +expired zone on a primary or a manually expired catalog zone becomes valid again +after a server configuration is reloaded or the :doc:`knotd<man_knotd>` process +is restarted, provided that the zone data hasn't been removed. + +.. _DNSSEC Key states: + +DNSSEC key states +================= + +During its lifetime, a DNSSEC key finds itself in different states. Most of the time it +is used for signing the zone and published in the zone. In order to exchange +the key, one type of a key rollover is necessary, and during this rollover, +the key goes through various states with respect to the rollover type and also the +state of the other key being rolled-over. + +First, let's list the states of the key being rolled-in. + +Standard states: + +- ``active`` — The key is used for signing. +- ``published`` — The key is published in the zone, but not used for signing. If the key is + a KSK or CSK, it is used for signing the DNSKEY RRSet. +- ``ready`` (only for KSK) — The key is published in the zone and used for signing. The + old key is still active, since we are waiting for the DS records in the parent zone to be + updated (i.e. "KSK submission"). + +Special states for algorithm rollover: + +- ``pre-active`` — The key is not yet published in the zone, but it's used for signing the zone. +- ``published`` — The key is published in the zone, and it's still used for signing since the + pre-active state. + +Second, we list the states of the key being rolled-out. + +Standard states: + +- ``retire-active`` — The key is still used for signing, and is published in the zone, waiting for + the updated DS records in parent zone to be acked by resolvers (KSK case) or synchronizing + with KSK during algorithm rollover (ZSK case). +- ``retired`` — The key is no longer used for signing. If ZSK, the key is still published in the zone. +- ``removed`` — The key is not used in any way (in most cases such keys are deleted immediately). + +Special states for algorithm rollover: + +- ``post-active`` — The key is no longer published in the zone, but still used for signing. + +Special states for :rfc:`5011` trust anchor roll-over + +- ``revoke`` (only for KSK) — The key is published and used for signing, and the Revoked flag is set. + +.. NOTE:: + Trust anchor roll-over is not implemented with automatic key management. + + The ``revoke`` state can only be established using :doc:`keymgr<man_keymgr>` when using + :ref:`dnssec-manual-key-management`. + +The states listed above are relevant for :doc:`keymgr<man_keymgr>` operations like generating +a key, setting its timers and listing KASP database. + +Note that the key "states" displayed in the server log lines while zone signing +are not according to those listed above, but just a hint as to what the key is currently used for +(e.g. "public, active" = key is published in the zone and used for signing). + +.. _DNSSEC Key rollovers: + +DNSSEC key rollovers +==================== + +This section describes the process of DNSSEC key rollover and its implementation +in Knot DNS, and how the operator might watch and check that it's working correctly. +The prerequisite is automatic zone signing with enabled +:ref:`automatic key management<dnssec-automatic-ksk-management>`. + +The KSK and ZSK rollovers are triggered by the respective zone key getting old according +to the settings (see :ref:`KSK<policy_ksk-lifetime>` and :ref:`ZSK<policy_zsk-lifetime>` lifetimes). + +The algorithm rollover starts when the policy :ref:`algorithm<policy_algorithm>` +field is updated to a different value. + +The signing scheme rollover happens when the policy :ref:`signing scheme<policy_single-type-signing>` +field is changed. + +It's also possible to change the algorithm and signing scheme in one rollover. + +The operator may check the next rollover phase time by watching the next zone signing time, +either in the log or via ``knotc zone-status``. There is no special log for finishing a rollover. + +.. NOTE:: + There are never two key rollovers running in parallel for one zone. If + a rollover is triggered while another is in progress, it waits until the + first one is finished. + +The ZSK rollover is performed with Pre-publish method, KSK rollover uses Double-Signature +scheme, as described in :rfc:`6781`. + +.. _Automatic KSK and ZSK rollovers example: + +Automatic KSK and ZSK rollovers example +--------------------------------------- + +Let's start with the following set of keys:: + + 2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, key, tag 50613, algorithm ECDSAP256SHA256, KSK, public, active + 2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, key, tag 62932, algorithm ECDSAP256SHA256, public, active + +The last fields hint the key state: ``public`` denotes a key that will be presented +as the DNSKEY record, ``ready`` means that CDS/CDNSKEY records were created, +``active`` tells us that the key is used for signing, while ``active+`` is an +active key undergoing a roll-over or roll-in. + +For demonstration purposes, the following configuration is used:: + + submission: + - id: test_submission + check-interval: 2s + parent: dnssec_validating_resolver + + policy: + - id: test_policy + ksk-lifetime: 5m + zsk-lifetime: 2m + propagation-delay: 2s + dnskey-ttl: 10s + zone-max-ttl: 15s + ksk-submission: test_submission + +Upon the zone's KSK lifetime expiration, a new KSK is generated and the rollover +continues along the lines of :rfc:`6781#section-4.1.2`:: + + # KSK Rollover (50613 -> 9081) + + 2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, signing zone + 2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, KSK rollover started + 2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, key, tag 50613, algorithm ECDSAP256SHA256, KSK, public, active + 2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, key, tag 62932, algorithm ECDSAP256SHA256, public, active + 2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, key, tag 9081, algorithm ECDSAP256SHA256, KSK, public, active+ + 2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, signing started + 2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, successfully signed + 2021-05-10T20:50:00+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:50:12+0200 + + ... (propagation-delay + dnskey-ttl) ... + + 2021-05-10T20:50:12+0200 info: [example.com.] DNSSEC, signing zone + 2021-05-10T20:50:12+0200 notice: [example.com.] DNSSEC, KSK submission, waiting for confirmation + 2021-05-10T20:50:12+0200 info: [example.com.] DNSSEC, key, tag 50613, algorithm ECDSAP256SHA256, KSK, public, active + 2021-05-10T20:50:12+0200 info: [example.com.] DNSSEC, key, tag 62932, algorithm ECDSAP256SHA256, public, active + 2021-05-10T20:50:12+0200 info: [example.com.] DNSSEC, key, tag 9081, algorithm ECDSAP256SHA256, KSK, public, ready, active+ + 2021-05-10T20:50:12+0200 info: [example.com.] DNSSEC, signing started + 2021-05-10T20:50:12+0200 info: [example.com.] DNSSEC, successfully signed + 2021-05-10T20:50:12+0200 info: [example.com.] DNSSEC, next signing at 2021-05-17T20:49:56+0200 + +At this point the new KSK has to be submitted to the parent zone. Knot detects the updated parent's DS +record automatically (and waits for additional period of the DS's TTL before retiring the old key) +if :ref:`parent DS check<Submission section>` is configured, otherwise the +operator must confirm it manually (using ``knotc zone-ksk-submitted``):: + + 2021-05-10T20:50:12+0200 info: [example.com.] DS check, outgoing, remote 127.0.0.1@5300, KSK submission check: negative + 2021-05-10T20:50:14+0200 info: [example.com.] DS check, outgoing, remote 127.0.0.1@5300, KSK submission check: negative + 2021-05-10T20:50:16+0200 info: [example.com.] DS check, outgoing, remote 127.0.0.1@5300, KSK submission check: positive + 2021-05-10T20:50:16+0200 notice: [example.com.] DNSSEC, KSK submission, confirmed + 2021-05-10T20:50:16+0200 info: [example.com.] DNSSEC, signing zone + 2021-05-10T20:50:16+0200 info: [example.com.] DNSSEC, key, tag 50613, algorithm ECDSAP256SHA256, KSK, public, active+ + 2021-05-10T20:50:16+0200 info: [example.com.] DNSSEC, key, tag 62932, algorithm ECDSAP256SHA256, public, active + 2021-05-10T20:50:16+0200 info: [example.com.] DNSSEC, key, tag 9081, algorithm ECDSAP256SHA256, KSK, public, active + 2021-05-10T20:50:16+0200 info: [example.com.] DNSSEC, signing started + 2021-05-10T20:50:16+0200 info: [example.com.] DNSSEC, successfully signed + 2021-05-10T20:50:16+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:50:23+0200 + + ... (parent's DS TTL is 7 seconds) ... + + 2021-05-10T20:50:23+0200 info: [example.com.] DNSSEC, signing zone + 2021-05-10T20:50:23+0200 info: [example.com.] DNSSEC, key, tag 62932, algorithm ECDSAP256SHA256, public, active + 2021-05-10T20:50:23+0200 info: [example.com.] DNSSEC, key, tag 9081, algorithm ECDSAP256SHA256, KSK, public, active + 2021-05-10T20:50:23+0200 info: [example.com.] DNSSEC, signing started + 2021-05-10T20:50:23+0200 info: [example.com.] DNSSEC, successfully signed + 2021-05-10T20:50:23+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:51:56+0200 + +Upon the zone's ZSK lifetime expiration, a new ZSK is generated and the rollover +continues along the lines of :rfc:`6781#section-4.1.1`:: + + # ZSK Rollover (62932 -> 33255) + + 2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, signing zone + 2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, ZSK rollover started + 2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, key, tag 62932, algorithm ECDSAP256SHA256, public, active + 2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, key, tag 9081, algorithm ECDSAP256SHA256, KSK, public, active + 2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, key, tag 33255, algorithm ECDSAP256SHA256, public + 2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, signing started + 2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, successfully signed + 2021-05-10T20:51:56+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:52:08+0200 + + ... (propagation-delay + dnskey-ttl) ... + + 2021-05-10T20:52:08+0200 info: [example.com.] DNSSEC, signing zone + 2021-05-10T20:52:08+0200 info: [example.com.] DNSSEC, key, tag 62932, algorithm ECDSAP256SHA256, public + 2021-05-10T20:52:08+0200 info: [example.com.] DNSSEC, key, tag 9081, algorithm ECDSAP256SHA256, KSK, public, active + 2021-05-10T20:52:08+0200 info: [example.com.] DNSSEC, key, tag 33255, algorithm ECDSAP256SHA256, public, active + 2021-05-10T20:52:08+0200 info: [example.com.] DNSSEC, signing started + 2021-05-10T20:52:08+0200 info: [example.com.] DNSSEC, successfully signed + 2021-05-10T20:52:08+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:52:25+0200 + + ... (propagation-delay + zone-max-ttl) ... + + 2021-05-10T20:52:25+0200 info: [example.com.] DNSSEC, signing zone + 2021-05-10T20:52:25+0200 info: [example.com.] DNSSEC, key, tag 9081, algorithm ECDSAP256SHA256, KSK, public, active + 2021-05-10T20:52:25+0200 info: [example.com.] DNSSEC, key, tag 33255, algorithm ECDSAP256SHA256, public, active + 2021-05-10T20:52:25+0200 info: [example.com.] DNSSEC, signing started + 2021-05-10T20:52:25+0200 info: [example.com.] DNSSEC, successfully signed + 2021-05-10T20:52:25+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:54:08+0200 + 2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, signing zone + +Further rollovers:: + + ... (zsk-lifetime - propagation-delay - zone-max-ttl) ... + + # Another ZSK Rollover (33255 -> 49526) + + 2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, signing zone + 2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, ZSK rollover started + 2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, key, tag 9081, algorithm ECDSAP256SHA256, KSK, public, active + 2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, key, tag 33255, algorithm ECDSAP256SHA256, public, active + 2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, key, tag 49526, algorithm ECDSAP256SHA256, public + 2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, signing started + 2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, successfully signed + 2021-05-10T20:54:08+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:54:20+0200 + + ... + + # Another KSK Rollover (9081 -> 9179) + + 2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, signing zone + 2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, KSK rollover started + 2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, key, tag 9081, algorithm ECDSAP256SHA256, KSK, public, active + 2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, key, tag 49526, algorithm ECDSAP256SHA256, public, active + 2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, key, tag 9179, algorithm ECDSAP256SHA256, KSK, public, active+ + 2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, signing started + 2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, successfully signed + 2021-05-10T20:55:00+0200 info: [example.com.] DNSSEC, next signing at 2021-05-10T20:55:12+0200 + + ... + +.. TIP:: + If systemd is available, the KSK submission event is logged into journald + in a structured way. The intended use case is to trigger a user-created script. + Example:: + + journalctl -f -t knotd -o json | python3 -c ' + import json, sys + for line in sys.stdin: + k = json.loads(line); + if "KEY_SUBMISSION" in k: + print("%s, zone=%s, keytag=%s" % (k["__REALTIME_TIMESTAMP"], k["ZONE"], k["KEY_SUBMISSION"])) + ' + +.. _DNSSEC Shared KSK: + +DNSSEC shared KSK +================= + +Knot DNS allows, with automatic DNSSEC key management, to configure a shared KSK for multiple zones. +By enabling :ref:`policy_ksk-shared`, we tell Knot to share all newly-created KSKs +among all the zones with the same :ref:`DNSSEC signing policy<Policy section>` assigned. + +The feature works as follows. Each zone still manages its keys separately. If a new KSK shall be +generated for the zone, it first checks if it can grab another zone's shared KSK instead - +that is the last generated KSK in any of the zones with the same policy assigned. +Anyway, only the cryptographic material is shared, the key may have different timers +in each zone. + +.. rubric:: Consequences: + +If we have an initial setting with brand new zones without any DNSSEC keys, +the initial keys for all zones are generated. With shared KSK, they will all have the same KSK, +but different ZSKs. The KSK rollovers may take place at slightly different times for each of the zones, +but the resulting new KSK will be shared again among all of them. + +If we have zones which already have their keys, turning on the shared KSK feature triggers no action. +But when a KSK rollover takes place, they will use the same new key afterwards. + +.. WARNING:: + Changing the policy :ref:`id<policy_id>` must be done carefully if shared + KSK is in use. + +.. _DNSSEC Delete algorithm: + +DNSSEC delete algorithm +======================= + +This is how to "disconnect" a signed zone from a DNSSEC-aware parent zone. +More precisely, we tell the parent zone to remove our zone's DS record by +publishing a special formatted CDNSKEY and CDS record. This is mostly useful +if we want to turn off DNSSEC on our zone so it becomes insecure, but not bogus. + +With automatic DNSSEC signing and key management by Knot, this is as easy as +configuring :ref:`policy_cds-cdnskey-publish` option and reloading the configuration. +We check if the special CDNSKEY and CDS records with the rdata "0 3 0 AA==" and "0 0 0 00", +respectively, appeared in the zone. + +After the parent zone notices and reflects the change, we wait for TTL expire +(so all resolvers' caches get updated), and finally we may do anything with the +zone, e.g. turning off DNSSEC, removing all the keys and signatures as desired. + +.. _DNSSEC Offline KSK: + +DNSSEC Offline KSK +================== + +Knot DNS allows a special mode of operation where the private part of the Key Signing Key is +not available to the daemon, but it is rather stored securely in an offline storage. This requires +that the KSK/ZSK signing scheme is used (i.e. :ref:`policy_single-type-signing` is off). +The Zone Signing Key is always fully available to the daemon in order to sign common changes to the zone contents. + +The server (or the "ZSK side") only uses ZSK to sign zone contents and its changes. Before +performing a ZSK rollover, the DNSKEY records will be pre-generated and signed by the +signer (the "KSK side"). Both sides exchange keys in the form of human-readable messages with the help +of the :doc:`keymgr<man_keymgr>` utility. + +Prerequisites +------------- + +For the ZSK side (i.e. the operator of the DNS server), the zone has to be configured with: + +- Enabled :ref:`DNSSEC signing <zone_dnssec-signing>` +- Properly configured and assigned :ref:`DNSSEC policy <Policy section>`: + + - Enabled :ref:`policy_manual` + - Enabled :ref:`policy_offline-ksk` + - Explicit :ref:`policy_dnskey-ttl` + - Explicit :ref:`policy_zone-max-ttl` + - Other options are optional +- KASP DB may contain a ZSK (the present or some previous one(s)) + +For the KSK side (i.e. the operator of the KSK signer), the zone has to be configured with: + +- Properly configured and assigned :ref:`DNSSEC policy <Policy section>`: + + - Enabled :ref:`policy_manual` + - Enabled :ref:`policy_offline-ksk` + - Optional :ref:`policy_rrsig-lifetime`, :ref:`policy_rrsig-refresh`, + :ref:`policy_algorithm`, :ref:`policy_reproducible-signing`, + and :ref:`policy_cds-cdnskey-publish` + - Other options are ignored +- KASP DB contains a KSK (the present or a newly generated one) + +Generating and signing future ZSKs +---------------------------------- + +1. Use the ``keymgr pregenerate`` command on the ZSK side to prepare the ZSKs for a specified period of time in the future. The following example + generates ZSKs for the *example.com* zone for 6 months ahead starting from now:: + + $ keymgr -c /path/to/ZSK/side.conf example.com. pregenerate +6mo + + If the time period is selected as e.g. *2 x* :ref:`policy_zsk-lifetime` *+ 4 x* :ref:`policy_propagation-delay`, it will + prepare roughly two complete future key rollovers. The newly-generated + ZSKs remain in non-published state until their rollover starts, i.e. the time + they would be generated in case of automatic key management. + +2. Use the ``keymgr generate-ksr`` command on the ZSK side to export the public parts of the future ZSKs in a form + similar to DNSKEY records. You might use the same time period as in the first step:: + + $ keymgr -c /path/to/ZSK/side.conf example.com. generate-ksr +0 +6mo > /path/to/ksr/file + + Save the output of the command (called the Key Signing Request or KSR) to a file and transfer it to the KSK side e.g. via e-mail. + +3. Use the ``keymgr sign-ksr`` command on the KSK side with the KSR file from the previous step as a parameter:: + + $ keymgr -c /path/to/KSK/side.conf example.com. sign-ksr /path/to/ksr/file > /path/to/skr/file + + This creates all the future forms of the DNSKEY, CDNSKEY and CSK records and all the respective RRSIGs and prints them on output. Save + the output of the command (called the Signed Key Response or SKR) to a file and transfer it back to the ZSK side. + +4. Use the ``keymgr import-skr`` command to import the records and signatures from the SKR file generated in the last step + into the KASP DB on the ZSK side:: + + $ keymgr -c /path/to/ZSK/side.conf example.com. import-skr /path/to/skr/file + +5. Use the ``knotc zone-keys-load`` command to trigger a zone re-sign on the ZSK-side and set up the future re-signing events correctly.:: + + $ knotc -c /path/to/ZSK/side.conf zone-keys-load example.com. + +6. Now the future ZSKs and DNSKEY records with signatures are ready in KASP DB for later usage. + Knot automatically uses them at the correct time intervals. + The entire procedure must be repeated before the time period selected at the beginning passes, + or whenever a configuration is changed significantly. Importing new SKR over some previously-imported + one leads to deleting the old offline records. + +Offline KSK and manual ZSK management +------------------------------------- + +If the automatically preplanned ZSK roll-overs (first step) are not desired, just set the :ref:`policy_zsk-lifetime` +to zero, and manually pregenerate ZSK keys and set their timers. Then follow the steps +``generate-ksr — sign-ksr — import-skr — zone-keys-load`` and repeat the ceremony when necessary. + +Offline KSK roll-over +--------------------- + +The KSKs (on the KSK side) must be managed manually, but manual KSK roll-over is possible. Just plan the steps +of the KSK roll-over in advance, and whenever the KSK set or timers are changed, re-perform the relevant rest of the ceremony +``sign-ksr — import-skr — zone-keys-load``. + +Emergency SKR +------------- + +A general recommendation for large deployments is to have some backup pre-published keys, so that if the current ones are +compromised, they can be rolled-over to the backup ones without any delay. But in the case of Offline KSK, according to +the procedures above, both ZSK and KSK immediate rollovers require the KSR-SKR ceremony. + +However, a trick can be done to achieve really immediate key substitution. This is no longer about Knot DNS functionality, +just a hint for the operator. + +The idea is to perform every KSR-SKR ceremony twice: once with normal state of the keys (the backup key is only published), +and once with the keys already exchanged (the backup key is temporarily marked as active and the standard key temporarily +as public only). The second (backup) SKR should be saved for emergency key replacement. + +Summary of the steps: + +* Prepare KSK and ZSK side as usual, including public-only emergency key +* Perform normal Offline KSK ceremony: + + * Pre-generate ZSKs (only in the case of automatic ZSK management) + * Generate KSR + * Sign KSR on the KSK side + * Import SKR + * Re-sign the zone + +* Freeze the zone on the ZSK side +* Temporarily set the backup key as active and the normal key as publish-only +* Perform backup Offline KSK ceremony: + + * Generate KSR (only if the backup key is a replacement for ZSK) + * Sign the KSR on the KSK side + * Save the SKR to a backup storage, don't import it yet + +* Return the keys to the previous state +* Thaw the zone on the ZSK side + +Emergency key replacement: + +* Import the backup SKR +* Align the keys with the new states (backup key as active, compromised key as public) +* Re-sign the zone + +.. _DNSSEC Import of keys to HSM: + +Import of keys to HSM +===================== + +Knot DNS stores DNSSEC keys in textual PEM format (:rfc:`7468`), +while many HSM management software require the keys for import to be in binary +DER format (`Rec. ITU-T X.690 <https://www.itu.int/ITU-T/recommendations/rec.aspx?rec=x.690>`_). +Keys can be converted from one format to another by software tools such as +``certtool`` from `GnuTLS <https://www.gnutls.org/>`_ suite or +``openssl`` from `OpenSSL <https://www.openssl.org/>`_ suite. + +In the examples below, ``c4eae5dea3ee8c15395680085c515f2ad41941b6`` is used as the key ID, +``c4eae5dea3ee8c15395680085c515f2ad41941b6.pem`` represents the filename of the key in PEM format +as copied from the Knot DNS zone's :ref:`KASP database directory <database_kasp-db>`, +``c4eae5dea3ee8c15395680085c515f2ad41941b6.priv.der`` represents the file containing the private +key in DER format as generated by the conversion tool, and +``c4eae5dea3ee8c15395680085c515f2ad41941b6.pub.der`` represents the file containing the public +key in DER format as generated by the conversion tool. + +.. code-block:: console + + $ certtool -V -k --outder --infile c4eae5dea3ee8c15395680085c515f2ad41941b6.pem \ + --outfile c4eae5dea3ee8c15395680085c515f2ad41941b6.priv.der + + $ certtool -V --pubkey-info --outder --load-privkey c4eae5dea3ee8c15395680085c515f2ad41941b6.pem \ + --outfile c4eae5dea3ee8c15395680085c515f2ad41941b6.pub.der + +As an alternative, ``openssl`` can be used instead. It is necessary to specify either ``rsa`` or ``ec`` +command according to the algorithm used by the key. + +.. code-block:: console + + $ openssl rsa -outform DER -in c4eae5dea3ee8c15395680085c515f2ad41941b6.pem \ + -out c4eae5dea3ee8c15395680085c515f2ad41941b6.priv.der + + $ openssl rsa -outform DER -in c4eae5dea3ee8c15395680085c515f2ad41941b6.pem \ + -out c4eae5dea3ee8c15395680085c515f2ad41941b6.pub.der -pubout + +Actual import of keys (both public and private keys from the same key pair) to an HSM can be done +via PKCS #11 interface, by ``pkcs11-tool`` from `OpenSC <https://github.com/OpenSC/OpenSC/wiki>`_ toolkit +for example. In the example below, ``/usr/local/lib/pkcs11.so`` is used as a name of the PKCS #11 library +or module used for communication with the HSM. + +.. code-block:: console + + $ pkcs11-tool --module /usr/local/lib/pkcs11.so --login \ + --write-object c4eae5dea3ee8c15395680085c515f2ad41941b6.priv.der --type privkey \ + --usage-sign --id c4eae5dea3ee8c15395680085c515f2ad41941b6 + + $ pkcs11-tool --module /usr/local/lib/pkcs11.so -login \ + --write-object c4eae5dea3ee8c15395680085c515f2ad41941b6.pub.der --type pubkey \ + --usage-sign --id c4eae5dea3ee8c15395680085c515f2ad41941b6 + +.. _Controlling a running daemon: + +Daemon controls +=============== + +Knot DNS was designed to allow server reconfiguration on-the-fly +without interrupting its operation. Thus it is possible to change +both configuration and zone files and also add or remove zones without +restarting the server. This can be done with:: + + $ knotc reload + +If you want to refresh the secondary zones, you can do this with:: + + $ knotc zone-refresh + +.. _Data and metadata backup: + +Data and metadata backup +======================== + +Some of the zone-related data, such as zone contents or DNSSEC signing keys, +and metadata, like zone timers, might be worth backing up. For the sake of +consistency, it's usually necessary to shut down the server, or at least freeze all +the zones, before copying the data like zone files, KASP database, etc, to +a backup location. To avoid this necessity, Knot DNS provides a feature to +back up some or all of the zones seamlessly. + +Online backup +------------- + +While the server is running and the zones normally loaded (even when they are +constantly/frequently being updated), the user can manually trigger the +backup by calling:: + + $ knotc zone-backup +backupdir /path/of/backup + +To back up just some of the zones (instead of all), the user might provide +their list:: + + $ knotc zone-backup +backupdir /path/to/backup zone1.com. zone2.com. ... + +The backup directory should be empty or non-existing and it must be accessible +and writable for the :ref:`server_user` account under which knotd is running. +The backup procedure will begin soon and will happen zone-by-zone +(partially in parallel if more :ref:`server_background-workers` are configured). +**The user shall check the logs for the outcome of each zone's backup attempt.** +The knotc's ``-b`` parameter might be used if the user desires to wait until +the backup work is done and a simple result status is printed out. + +.. TIP:: + There is a plain ASCII text file in the backup directory, + ``knot_backup.label``, that contains some useful information about the + backup, such as the backup creation date & time, the server identity, etc. + Care must always be taken **not to remove this file** from the backup nor to + damage it. + +Offline restore +--------------- + +If the Online backup was performed for all zones, it's possible to +restore the backed up data by simply copying them to their normal locations, +since they're simply copies. For example, the user can copy (overwrite) +the backed up KASP database files to their configured location. + +This restore of course must be done when the server is stopped. After starting up +the server, it should run in the same state as at the time of backup. + +This method is recommended in the case of complete data loss, for example +physical server failure. + +.. NOTE:: + The online backup procedure stores all zone files in a single directory + using their default file names. If the original directory layout was + different, then the required directory structure must be created manually + for offline restore and zone files must be placed individually to their + respective directories. If the zone file names don't follow the default + pattern, they must be renamed manually to match the configuration. These + limitations don't apply to the online restore procedure. + +Online restore +-------------- + +This procedure is symmetrical to Online backup. By calling:: + + $ knotc zone-restore +backupdir /path/of/backup + +the user triggers a one-by-one zone restore from the backup on a running +server. Again, a subset of zones might be specified. It must be specified +if the backup was created for only a subset of zones. + +.. NOTE:: + For restore of backups that have been created by Knot DNS releases prior + to 3.1, it's necessary to use the ``-f`` option. Since this option also + turns off some verification checks, it shouldn't be used in other cases. + +Limitations +----------- + +Neither configuration file nor :ref:`Configuration database` is backed up +by zone backup. The configuration has to be synchronized before zone restore +is performed! + +If the private keys are stored in a HSM (anything using a PKCS#11 interface), +they are not backed up. This includes internal metadata of the PKCS#11 provider +software, such as key mappings, authentication information, and the configuration +of the provider. Details are vendor-specific. + +The restore procedure does not care for keys deleted after taking the snapshot. +Thus, after restore, there might remain some redundant ``.pem`` files +of obsolete signing keys. + +.. TIP:: + In order to seamlessly deploy a restored backup of KASP DB with respect to + a possibly ongoing DNSSEC key rollover, it's recommended to set + :ref:`propagation-delay <policy_propagation-delay>` to the sum of: + + - The maximum delay between beginning of the zone signing and publishing + re-signed zone on all public secondary servers. + - How long it takes for the backup server to start up with the restored data. + - The period between taking backup snapshots of the live environment. + +.. _Statistics: + +Statistics +========== + +The server provides some general statistics and optional query module statistics +(see :ref:`mod-stats<mod-stats>`). + +Server statistics or global module statistics can be shown by:: + + $ knotc stats + $ knotc stats server # Show all server counters + $ knotc stats mod-stats # Show all mod-stats counters + $ knotc stats server.zone-count # Show specific server counter + +Per zone statistics can be shown by:: + + $ knotc zone-stats example.com mod-stats + +To show all supported counters even with 0 value, use the force option. + +A simple periodic statistic dump to a YAML file can also be enabled. See +:ref:`stats section` for the configuration details. + +As the statistics data can be accessed over the server control socket, +it is possible to create an arbitrary script (Python is supported at the moment) +which could, for example, publish the data in JSON format via HTTP(S) +or upload the data to a more efficient time series database. Take a look into +the python folder of the project for these scripts. + +.. _Mode XDP: + +Mode XDP +======== + +Thanks to recent Linux kernel capabilities, namely eXpress Data Path and AF_XDP +address family, Knot DNS offers a high-performance DNS over UDP packet processing +mode. The basic idea is to filter DNS messages close to the network device and +effectively forward them to the nameserver without touching the network stack +of the operating system. Other messages (including DNS over TCP) are processed +as usual. + +If :ref:`xdp_listen` is configured, the server creates +additional XDP workers, listening on specified interface(s) and port(s) for DNS +over UDP queries. Each XDP worker handles one RX and TX network queue pair. + +.. _Mode XDP_pre-requisites: + +Pre-requisites +-------------- + +* Linux kernel 4.18+ (5.x+ is recommended for optimal performance) compiled with + the `CONFIG_XDP_SOCKETS=y` option. The XDP mode isn't supported in other operating systems. +* A multiqueue network card, which offers enough Combined RX/TX channels, with + native XDP support is highly recommended. Successfully tested cards: + + * Intel series 700 (driver `i40e`), maximum number of channels per interface is 64. + * Intel series 500 (driver `ixgbe`), maximum number of channels per interface is 64. + The number of CPUs available has to be at most 64! + +* If the `knotd` service is not directly executed in the privileged mode, some + additional Linux capabilities have to be set: + + Execute command:: + + systemctl edit knot + + And insert these lines:: + + [Service] + CapabilityBoundingSet=CAP_NET_RAW CAP_NET_ADMIN CAP_SYS_ADMIN CAP_IPC_LOCK CAP_SYS_RESOURCE + AmbientCapabilities=CAP_NET_RAW CAP_NET_ADMIN CAP_SYS_ADMIN CAP_IPC_LOCK CAP_SYS_RESOURCE + + The `CAP_SYS_RESOURCE` is needed on Linux < 5.11. + + All the capabilities are dropped upon the service is started. + +* For proper processing of VLAN traffic, VLAN offloading should be disabled. E.g.:: + + ethtool -K <interface> tx-vlan-offload off rx-vlan-offload off + + +Optimizations +------------- + +Some helpful commands:: + + ethtool -N <interface> rx-flow-hash udp4 sdfn + ethtool -N <interface> rx-flow-hash udp6 sdfn + ethtool -L <interface> combined <?> + ethtool -G <interface> rx <?> tx <?> + renice -n 19 -p $(pgrep '^ksoftirqd/[0-9]*$') + +Limitations +----------- + +* Request and its response must go through the same physical network device. +* Dynamic DNS over XDP is not supported. +* MTU higher than 1790 bytes is not supported. +* Multiple BPF filters per one network device are not supported. +* Systems with big-endian byte ordering require special recompilation of the nameserver. +* IPv4 header and UDP checksums are not verified on received DNS messages. +* DNS over XDP traffic is not visible to common system tools (e.g. firewall, tcpdump etc.). +* BPF filter is not automatically unloaded from the network device. Manual filter unload:: + + ip link set dev <interface> xdp off |