.. 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` 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` 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` 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) ========================= Some types of incoming DNS requests must be authorized before they can be processed by the server. A zone can have configured :ref:`zone_acl` which is a sequence of :ref:`rules ` describing what requests are authorized. By default if :ref:`automatic ACL ` is not enabled, all requests, which require authorization, are denied. Every ACL rule can allow or deny one or more request types based on the source IP address, network subnet, or address range and/or if the request is secured by a given TSIG key. See :doc:`keymgr -t` on how to generate a TSIG key. If there are multiple ACL rules assigned to a zone, they are applied in the specified order of the :ref:`zone_acl` configuration. The first rule that matches the given request is applied and the remaining rules are ignored. Some examples:: 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] # Allow some addresses with an exception :: key: - id: key1 # The real TSIG key name algorithm: hmac-sha256 secret: 4Tc0K1QkcMCs7cOW2LuSWnxQY0qysdvsZlSb4yTN9pA= 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] # Allow with the TSIG except for the subnet In the case of dynamic DNS updates, some additional conditions may be specified for more granular filtering. See more in the section :ref:`Restricting dynamic updates`. .. 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`. 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. For effective zone synchronization, incoming zone change notifications (NOTIFY), which require authorization, can be enabled using :ref:`automatic ACL ` or :ref:`explicit ACL ` configuration. Optional transaction authentication (TSIG) is supported for both zone transfers and zone notifications:: server: automatic-acl: on # Enabled automatic ACL key: - id: xfr_notify_key # Common TSIG key for XFR an NOTIFY algorithm: hmac-sha256 secret: VFRejzw8h4M7mb0xZKRFiZAfhhd1eDGybjqHr2FV3vc= remote: - id: primary address: [2001:DB8:1::1, 192.168.1.1] # Primary server IP addresses # via: [2001:DB8:2::1, 10.0.0.1] # Local source addresses (optional) key: xfr_notify_key # TSIG key (optional) zone: - domain: example.com master: primary # Primary remote(s) An example of explicit ACL with different TSIG keys for zone transfers and notifications:: key: - id: notify_key # TSIG key for NOTIFY algorithm: hmac-sha256 secret: uBbhV4aeSS4fPd+wF2ZIn5pxOMF35xEtdq2ibi2hHEQ= - id: xfr_key # TSIG key for XFR algorithm: hmac-sha256 secret: VFRejzw8h4M7mb0xZKRFiZAfhhd1eDGybjqHr2FV3vc= remote: - id: primary address: [2001:DB8:1::1, 192.168.1.1] # Primary server IP addresses # via: [2001:DB8:2::1, 10.0.0.1] # Local source addresses if needed key: xfr_key # Optional TSIG key acl: - id: notify_from_primary # ACL rule for NOTIFY from primary address: [2001:DB8:1::1, 192.168.1.1] # Primary addresses (optional) key: notify_key # TSIG key (optional) action: notify zone: - domain: example.com master: primary # Primary remote(s) acl: notify_from_primary # Explicit ACL(s) Note that the :ref:`zone_master` option accepts a list of remotes, which are queried for a zone refresh sequentially in the specified order. When the server receives a zone change notification from a listed remote, only that remote is used for a subsequent zone transfer. .. 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 ===================== A zone is considered primary if it doesn't have :ref:`zone_master` set. As outgoing zone transfers (XFR) require authorization, it must be enabled using :ref:`automatic ACL ` or :ref:`explicit ACL ` configuration. Outgoing zone change notifications (NOTIFY) to remotes can be set by configuring :ref:`zone_notify`. Transaction authentication (TSIG) is supported for both zone transfers and zone notifications:: server: automatic-acl: on # Enabled automatic ACL key: - id: xfr_notify_key # Common TSIG key for XFR an NOTIFY algorithm: hmac-sha256 secret: VFRejzw8h4M7mb0xZKRFiZAfhhd1eDGybjqHr2FV3vc= remote: - id: secondary address: [2001:DB8:1::1, 192.168.1.1] # Secondary server IP addresses # via: [2001:DB8:2::1, 10.0.0.1] # Local source addresses (optional) key: xfr_notify_key # TSIG key (optional) acl: - id: local_xfr # Allow XFR to localhost without TSIG address: [::1, 127.0.0.1] action: transfer zone: - domain: example.com notify: secondary # Secondary remote(s) acl: local_xfr # Explicit ACL for local XFR Note that the :ref:`zone_notify` option accepts a list of remotes, which are all notified sequentially in the specified order. A secondary zone may serve as a primary zone for a different set of remotes at the same time. 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 acl: update_acl .. _Restricting dynamic updates: Restricting dynamic updates --------------------------- There are several additional ACL options for dynamic DNS updates which affect the request classification based on the update contents. Updates can be restricted to specific resource record types:: acl: - id: type_rule action: update update-type: [A, AAAA, MX] # Updated records must match one of the specified types Another possibility is restriction on the owner name of updated records. The option :ref:`acl_update-owner` is used to select the source of domain names which are used for the comparison. And the option :ref:`acl_update-owner-match` specifies the required relation between the record owner and the reference domain names. Example:: acl: - id: owner_rule1 action: update update-owner: name # Updated record owners are restricted by the next conditions update-owner-match: equal # The record owner must exactly match one name from the next list update-owner-name: [foo, bar.] # Reference domain names .. NOTE:: If the specified owner name is non-FQDN (e.g. ``foo``), it's considered relatively to the effective zone name. So it can apply to more zones (e.g. ``foo.example.com.`` or ``foo.example.net.``). Alternatively, if the name is FQDN (e.g. ``bar.``), the rule only applies to this name. If the reference domain name is the zone name, the following variant can be used:: acl: - id: owner_rule2 action: update update-owner: zone # The reference name is the zone name update-owner-match: sub # Any record owner matches except for the zone name itself template: - id: default acl: owner_rule2 zone: - domain: example.com. - domain: example.net. The last variant is for the cases where the reference domain name is a TSIG key name, which must be used for the transaction security:: key: - id: example.com # Key names are always considered FQDN ... - id: steve.example.net ... - id: jane.example.net ... acl: - id: owner_rule3_com action: update update-owner: key # The reference name is the TSIG key name update-owner-match: sub # The record owner must be a subdomain of the key name key: [example.com] # One common key for updating all non-apex records - id: owner_rule3_net action: update update-owner: key # The reference name is the TSIG key name update-owner-match: equal # The record owner must exactly match the used key name key: [steve.example.net, jane.example.net] # Keys for updating specific zone nodes zone: - domain: example.com. acl: owner_rule3_com - domain: example.net. acl: owner_rule3_net .. _dnssec: Automatic DNSSEC signing ======================== Knot DNS supports automatic DNSSEC signing of zones. The signing can operate in two modes: 1. :ref:`Automatic key 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 `. 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` 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: custom_policy signing-threads: 4 algorithm: ECDSAP256SHA256 zsk-lifetime: 60d zone: - domain: myzone.test dnssec-signing: on dnssec-policy: custom_policy 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. .. _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 `, 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: custom_policy signing-threads: 4 algorithm: ECDSAP256SHA256 zsk-lifetime: 60d ksk-lifetime: 365d ksk-submission: parent_zone_sbm zone: - domain: myzone.test dnssec-signing: on dnssec-policy: custom_policy 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. .. _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` 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 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`: .. code-block:: console $ keymgr myzone.test. set 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 `_. 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. A *catalog-member zone* (or just *member zone*) is a zone based on information from the catalog zone and not from configuration file/database. *Member properties* are some additional information related to each member zone, also distributed with the catalog zone. 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 is useless as the zone won't be queried by clients), 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 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 format ``unique-id.zones.catalog. 0 IN PTR member.com.`` (but not ``too.deep.zones.catalog.``!) are processed and member zones created, with zone names taken from the PTR records' RData, and zone settings taken from the configuration templates specified by :ref:`zone_catalog-template`. The owner names of the PTR records shall follow this scheme: .. code-block:: console .zones.. where the mentioned labels shall match: - ** — Single label that is recommended to be unique among member zones. - ``zones`` — Required label. - ** — Name of the catalog zone. Additionally, records in the format ``group.unique-id.zones.catalog. 0 IN TXT "conf-template"`` are processed as a definition of the member's *group* property. The ``unique-id`` must match the one of the PTR record defining the member. All other records and other member properties 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 must be present as for any other zone. The version record ``version 0 IN TXT "2"`` is required at the catalog zone apex. 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. The catalog zone must have at least one :ref:`zone_catalog-template` configured. The configuration for any defined member zone is taken from its *group* property value, which should match some catalog-template name. If the *group* property is not defined for a member, is empty, or doesn't match any of defined catalog-template names, the first catalog-template (in the order from configuration) is used. Nesting of catalog zones isn't supported. 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. Any member zone, whose PTR record's owner has been changed, is purged immediately if and only if the ** has been changed. 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. .. NOTE:: Whenever a catalog zone is updated, the server reloads itself with all configured zones, including possibly existing other catalog zones. It's similar to calling `knotc zone-reload` (for all zones). The consequence is that new zone files might be discovered and reloaded, even for zones that do not relate to updated catalog zone. Catalog zones never expire automatically, regardless of what is declared in the catalog zone SOA. However, a catalog zone can be expired manually at any time using `knotc -f zone-purge +expire`. Currently, expiration of a catalog zone doesn't have any effect on its member zones. This will likely change in the future depending on the Internet Draft. .. WARNING:: The server 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` 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). Catalog zones configuration examples ------------------------------------ Below are configuration snippets (e.g. `server` and `log` sections missing) of very simple catalog zone setups, in order to illustrate the relations between catalog-related configuration options. First setup represents a very simple scenario where the primary is the catalog zone generator and the secondary is the catalog zone consumer. Primary configuration:: acl: - id: slave_xfr address: ... action: transfer template: - id: mmemb catalog-role: member catalog-zone: catz. acl: slave_xfr zone: - domain: catz. catalog-role: generate acl: slave_xfr - domain: foo.com. template: mmemb - domain: bar.com. template: mmemb Secondary configuration:: acl: - id: master_notify address: ... action: notify template: - id: smemb master: master acl: master_notify zone: - domain: catz. master: master acl: master_notify catalog-role: interpret catalog-template: smemb When new zones are added (or removed) to the primary configuration with assigned `mmemb` template, they will automatically propagate to the secondary and have the `smemb` template assigned there. Second example is with a hand-written (or script-generated) catalog zone, while employing configuration groups:: catz. 0 SOA invalid. invalid. 1625079950 3600 600 2147483646 0 catz. 0 NS invalid. version.catz. 0 TXT "2" nj2xg5bnmz2w4ltd.zones.catz. 0 PTR just-fun.com. group.nj2xg5bnmz2w4ltd.zones.catz. 0 TXT unsigned nvxxezjnmz2w4ltd.zones.catz. 0 PTR more-fun.com. group.nvxxezjnmz2w4ltd.zones.catz. 0 TXT unsigned nfwxa33sorqw45bo.zones.catz. 0 PTR important.com. group.nfwxa33sorqw45bo.zones.catz. 0 TXT signed mjqw42zomnxw2lq0.zones.catz. 0 PTR bank.com. group.mjqw42zomnxw2lq0.zones.catz. 0 TXT signed And the server in this case is configured to distinguish the groups by applying different templates:: template: - id: unsigned ... - id: signed dnssec-signing: on dnssec-policy: ... ... zone: - domain: catz. file: ... catalog-role: interpret catalog-template: [ unsigned, signed ] .. _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.