.. 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. 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. 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. Access control list (ACL) ========================= An ACL list specifies which remotes are allowed to send the server a specific request. A remote can be a single IP address or a network subnet. Also a TSIG key can be assigned (see :doc:`keymgr ` how to generate a TSIG key):: key: - id: key1 algorithm: hmac-md5 secret: Wg== acl: - id: address_rule address: [2001:db8::1, 192.168.2.0/24] # Allowed IP address list action: [transfer, update] # Allow zone transfers and updates - id: deny_rule # Negative match rule address: 192.168.2.100 action: transfer deny: on # The request is denied - id: key_rule key: key1 # Access based just on TSIG key action: transfer These rules can then be referenced from a zone :ref:`zone_acl`:: zone: - domain: example.com acl: [address_rule, deny_rule, key_rule] Slave zone ========== Knot DNS doesn't strictly differ between master and slave zones. The only requirement is to have a :ref:`master` statement set for the given zone. Also note that you need to explicitly allow incoming zone changed notifications via ``notify`` :ref:`acl_action` through 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 ` and :ref:`ACL ` 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 when all available ports are in the TIME_WAIT state, thus the transfers seize 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 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 Dynamic updates =============== Dynamic updates for the zone are allowed via proper ACL rule with the ``update`` action. If the zone is configured as a slave and a DNS update message is accepted, the server forwards the message to its primary master. The master's response is then forwarded back to the originator. However, if the zone is configured as a master, 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 Response rate limiting ====================== Response rate limiting (RRL) is a method to combat DNS reflection amplification attacks. These attacks rely on the fact that source address of a UDP query can be forged, and without a worldwide deployment of `BCP38 `_, such a forgery cannot be prevented. An attacker can use a DNS server (or multiple servers) as an amplification source and can flood a victim with a large number of unsolicited DNS responses. The RRL lowers the amplification factor of these attacks by sending some of the responses as truncated or by dropping them altogether. You can enable RRL by setting the :ref:`server_rate-limit` option in the :ref:`server section`. The option controls how many responses per second are permitted for each flow. Responses exceeding this rate are limited. The option :ref:`server_rate-limit-slip` then configures how many limited responses are sent as truncated (slip) instead of being dropped. :: server: rate-limit: 200 # Allow 200 resp/s for each flow rate-limit-slip: 2 # Every other response slips .. _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 `. 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 simply a directory in the file-system containing files in the JSON format. .. 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 week. .. _dnssec-automatic-key-management: Automatic key management ------------------------ For automatic key management, a signing 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.). The policy can be configured in the :ref:`policy section `, or a ``default`` policy with the default parameters can be used. A minimal zone configuration may look as follows:: zone: - domain: myzone.test dnssec-signing: on dnssec-policy: default With 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 zone key import`` 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 resigned at all. .. _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. Let's use the Single-Type Signing scheme with two algorithms, which is a scheme currently not supported by the automatic key management. Run: .. code-block:: console $ keymgr zone key generate myzone.test algorithm RSASHA256 size 1024 $ keymgr zone key generate myzone.test algorithm ECDSAP256SHA256 size 256 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 RSA key. Generate a new RSA key, but do not activate it yet: .. code-block:: console $ keymgr zone key generate myzone.test algorithm RSASHA256 size 1024 active +1d Take the key ID (or key tag) of the old RSA key and disable it the same time the new key gets activated: .. code-block:: console $ keymgr zone key set myzone.test retire +1d remove +1d Reload the server again. The new key will be published (i.e. the DNSKEY record will be added into the zone). Do not forget to update the DS record in the parent zone to include a reference to the new RSA key. This must happen in one day (in this case) including a delay required to propagate the new DS to caches. Note that as the ``+1d`` time specification is computed from the current time, the key replacement will not happen at once. First, a new key will be activated. A few moments later, the old key will be deactivated and removed. You can use exact time specification to make these two actions happen in one go. .. _dnssec-signing: Zone signing ------------ The signing process consists of the following steps: #. Processing KASP database events. (e.g. performing a step of a rollover). #. Fixing the NSEC or NSEC3 chain. #. 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). #. 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 resigning SOA record. The signing is initiated on the following occasions: - Start of the server - Zone reload - Reaching the signature refresh period - Received DDNS update - Forced zone resign via server control interface On a forced zone resign, all signatures in the zone are dropped and recreated. The ``knotc zone-status`` command can be used to see when the next scheduled DNSSEC resign will happen. .. _dnssec-limitations: Limitations ----------- The current DNSSEC implementation in Knot DNS has some limitations. Most of the limitations will be hopefully removed in the near future. - Automatic key management: - Only one DNSSEC algorithm can be used per zone. - Single-Type Signing scheme is not supported. - ZSK rollover always uses key pre-publish method (actually a feature). - KSK rollover is not implemented. - Signing: - Signature expiration jitter is not implemented. - Signature expiration skew is not implemented. - Utilities: - Legacy key import requires a private key. - Legacy key export is not implemented. - DS record export is not implemented.