Operational instructions

Several How to’s describe operational practices with DNSSEC:

Below, frequently used commands are described:

Publishing a DS

To publish a DS to a parent zone, utilize pdnsutil show-zone and take the DS from its output, and transfer it securely to your parent zone.

Going insecure

pdnsutil disable-dnssec ZONE

Warning

Going insecure with a zone that has a DS record in the parent zone will make the zone BOGUS. Make sure the parent zone removes the DS record before going insecure.

Setting the NSEC modes and parameters

As stated earlier, PowerDNS uses NSEC by default. If you want to use NSEC3 instead, issue:

pdnsutil set-nsec3 ZONE [PARAMETERS]

e.g.

pdnsutil set-nsec3 example.net '1 0 1 ab'

The quoted part is the content of the NSEC3PARAM records, as defined in 5155, in order:

  • Hash algorithm, should always be 1 (SHA1)
  • Flags, set to 1 for NSEC3 Opt-out, this best set as 0
  • Number of iterations of the hash function, read RFC 5155, Section 10.3 for recommendations
  • Salt to apply during hashing, in hexadecimal, or - to use no salt

To convert a zone from NSEC3 to NSEC operations, run:

pdnsutil unset-nsec3 ZONE

Warning

Don’t change from NSEC to NSEC3 (or the other way around) for zones with algorithm 5 (RSASHA1), 6 (DSA-NSEC3-SHA1) or 7 (RSASHA1-NSEC3-SHA1).

SOA-EDIT: ensure signature freshness on slaves

As RRSIGs can expire, slave servers need to know when to re-transfer the zone. In most implementations (BIND, NSD), this is done by re-signing the full zone outside of the nameserver, increasing the SOA serial and serving the new zone on the master.

With PowerDNS in Live-signing mode, the SOA serial is not increased by default when the RRSIG dates are rolled.

For zones that use Native replication replication PowerDNS will serve valid RRSIGs on all servers.

For master zones (where replication happens by means of AXFR), PowerDNS slaves will automatically re-transfer the zone when it notices the RRSIGs have changed, even when the SOA serial is not increased. This ensures the zone never serves old signatures.

If your DNS setup uses non-PowerDNS slaves, the slaves need to know when the signatures have been updated. This can be accomplished by setting the SOA-EDIT metadata for DNSSEC signed zones. This value controls how the value of the SOA serial is modified by PowerDNS.

Note

The SOA serial in the datastore will be untouched, SOA-EDIT is applied to DNS answers with the SOA record.

The default-soa-edit or default-soa-edit-signed configuration options can instead be set to ensure SOA-EDIT is set for every zone.

Possible SOA-EDIT values

The ‘inception’ refers to the time the RRSIGs got updated in live-signing mode. This happens every week (see Signatures). The inception time does not depend on local timezone, but some modes below will use localtime for representation.

INCREMENT-WEEKS

Increments the serial with the number of weeks since the UNIX epoch. This should work in every setup; but the result won’t look like YYYYMMDDSS anymore.

For example: a serial of 12345678 will become 12348079 on Wednesday 13th of January 2016 (2401 weeks after the epoch).

INCEPTION-EPOCH

Sets the new SOA serial number to the maximum of the old SOA serial number, and age in seconds of the last inception. This requires your backend zone to use the number of seconds since the UNIX epoch as SOA serial. The result is still the age in seconds of the last change to the zone, either by operator changes to the zone or the ‘addition’ of new RRSIGs.

As an example, a serial of 12345678 becomes 1452124800 on Wednesday 13th of January 2016.

INCEPTION-INCREMENT

Uses YYYYMMDDSS format for SOA serial numbers. If the SOA serial from the backend is within two days after inception, it gets incremented by two (the backend should keep SS below 98). Otherwise it uses the maximum of the backend SOA serial number and inception time in YYYYMMDD01 format. This requires your backend zone to use YYYYMMDDSS as SOA serial format. Uses localtime to find the day for inception time.

This changes a serial of 2015120810 to 2016010701 on Wednesday 13th of January 2016.

EPOCH

Sets the SOA serial to the number of seconds since the epoch.

Warning

Don’t combine this with AXFR - the slaves would keep refreshing all the time. If you need fast updates, sync the backend databases directly with incremental updates (or use the same database server on the slaves)

NONE

Ignore default-soa-edit and/or default-soa-edit-signed settings.

Security

During typical PowerDNS operation, the private part of the signing keys are ‘online’, which can be compared to operating an HTTPS server, where the private key is available on the webserver for cryptographic purposes.

In some settings, having such (private) keying material available online is considered undesirable. In this case, consider running in pre-signed mode.

Performance

DNSSEC has a performance impact, mostly measured in terms of additional memory used for the signature caches. In addition, on startup or AXFR-serving, a lot of signing needs to happen.

Most best practices are documented in RFC 6781.