TSIG

TSIG, as defined in RFC 2845, is a method for signing DNS messages using shared secrets. Each TSIG shared secret has a name, and PowerDNS can be told to allow zone transfer of a domain if the request is signed with an authorized name.

In PowerDNS, TSIG shared secrets are stored by the various backends. In case of the Generic SQL Backends, they can be found in the ‘tsigkeys’ table. The name can be chosen freely, but the algorithm name will typically be ‘hmac-md5’. Other supported algorithms are ‘hmac-sha1’, ‘hmac-shaX’ where X is 224, 256, 384 or 512. The content is a Base64-encoded secret.

Note

Most backends require DNSSEC support enabled to support TSIG. For the Generic SQL Backend make sure to use the DNSSEC enabled schema and to turn on the relevant ‘-dnssec’ flag (for example, gmysql-dnssec)!

Provisioning outbound AXFR access

To actually provision a named secret permission to AXFR a zone, set a metadata item in the ‘domainmetadata’ table called TSIG-ALLOW-AXFR with the key name in the content field. For example:

insert into tsigkeys (name, algorithm, secret) values ('test', 'hmac-md5', 'kp4/24gyYsEzbuTVJRUMoqGFmN3LYgVDzJ/3oRSP7ys=');
select id from domains where name='powerdnssec.org';
5
insert into domainmetadata (domain_id, kind, content) values (5, 'TSIG-ALLOW-AXFR', 'test');

$ dig -t axfr powerdnssec.org @127.0.0.1 -y 'test:kp4/24gyYsEzbuTVJRUMoqGFmN3LYgVDzJ/3oRSP7ys='

Warning

Any host with the correct TSIG key will be able to perform the AXFR, even if the host is not within the defined allow-axfr-ips ranges.

Another way of importing and activating TSIG keys into the database is using pdnsutil:

pdnsutil import-tsig-key test hmac-md5 'kp4/24gyYsEzbuTVJRUMoqGFmN3LYgVDzJ/3oRSP7ys='
pdnsutil activate-tsig-key powerdnssec.org test master

To ease interoperability, the equivalent configuration above in BIND would look like this:

key test. {
        algorithm hmac-md5;
        secret "kp4/24gyYsEzbuTVJRUMoqGFmN3LYgVDzJ/3oRSP7ys=";
};

zone "powerdnssec.org" {
    type master;
    file "powerdnssec.org";
    allow-transfer {  key test.; };
};

A packet authorized and authenticated by a TSIG signature will gain access to a zone even if the remote IP address is not otherwise allowed to AXFR a zone.

Provisioning signed notification and AXFR requests

To configure PowerDNS to send out TSIG signed AXFR requests for a zone to its master(s), set the AXFR-MASTER-TSIG metadata item for the relevant domain to the key that must be used.

The actual TSIG key must also be provisioned, as outlined in the previous section.

For the Generic SQL backends, configuring the use of TSIG for AXFR requests could be achieved as follows:

insert into tsigkeys (name, algorithm, secret) values ('test', 'hmac-md5', 'kp4/24gyYsEzbuTVJRUMoqGFmN3LYgVDzJ/3oRSP7ys=');
select id from domains where name='powerdnssec.org';
5
insert into domainmetadata (domain_id, kind, content) values (5, 'AXFR-MASTER-TSIG', 'test');

This can also be done using pdnsutil:

pdnsutil import-tsig-key test hmac-md5 'kp4/24gyYsEzbuTVJRUMoqGFmN3LYgVDzJ/3oRSP7ys='
pdnsutil activate-tsig-key powerdnssec.org test slave

This setup corresponds to the TSIG-ALLOW-AXFR access rule defined in the previous section.

In the interest of interoperability, the configuration above is (not quite) similar to the following BIND statements:

key test. {
        algorithm hmac-md5;
        secret "kp4/24gyYsEzbuTVJRUMoqGFmN3LYgVDzJ/3oRSP7ys=";
};

server 127.0.0.1 {
        keys { test.; };
};

zone "powerdnssec.org" {
 type slave;
 masters { 127.0.0.1; };
 file "powerdnssec.org";
};

Except that in this case, TSIG will be used for all communications with the master, not just those about AXFR requests.

GSS-TSIG support

GSS-TSIG allows authentication and authorization of DNS updates or AXFR using Kerberos with TSIG signatures.

Note

This feature is experimental and subject to change in future releases.

Prerequisites

  • Working Kerberos environment. Please refer to your Kerberos vendor documentation on how to set it up.
  • Service Principal(s) (of the form DNS/your.dns.server.name@REALM) in either per-user keytab or system keytab, where your.dns.server.name must match the nameserver name in the SOA record of the zone. If a user keytab is used, specify it using the KRB5_KTNAME environment variable when starting up PDNS server, which must be able to read the keytab file.

In particular, if something does not work, read logs and ensure that your kerberos environment is ok before filing an issue. Most common problems are time synchronization or changes done to the principal.

Setting up

To allow AXFR / DNS update to work, you need to set enable-gss-tsig and configure GSS-ACCEPTOR-PRINCIPAL in Per zone settings: Domain Metadata. This will define the principal that is used to accept any GSS context requests for names in the specified domain. This must match to a principal in the keytab used by PDNS Server. Next you need to define one or more GSS-ALLOW-AXFR-PRINCIPAL entries for AXFR, or TSIG-ALLOW-DNSUPDATE entries for DNS update. These must be set to the exact initiator (client) principal names you intend to allow either AXFR or DNS update. No wildcards accepted. If a Lua update policy is defined (see Dynamic DNS Update (RFC2136)) no TSIG-ALLOW-DNSUPDATE entries are needed, as the Lua policy defines which principals can update which records.