Bind 9 Administrator Reference Manual

Chapter 4. Advanced Concepts

4.1. Dynamic Update

Dynamic update is the term used for the ability under certain speciﬁed conditions to add, modify or

delete records or RRsets in the master zone ﬁles. Dynamic update is fully described in RFC 2136.

Dynamic update is enabled on a zone-by-zone basis, by including an allow-update or update-policy

clause in the zone statement.

Updating of secure zones (zones using DNSSEC) follows RFC 3007: SIG and NXT records affected by

updates are automatically regenerated by the server using an online zone key. Update authorization is

based on transaction signatures and an explicit server policy.

4.1.1. The journal ﬁle

All changes made to a zone using dynamic update are stored in the zone’s journal ﬁle. This ﬁle is

automatically created by the server when when the ﬁrst dynamic update takes place. The name of the

journal ﬁle is formed by appending the extension .jnl to the name of the corresponding zone ﬁle. The

journal ﬁle is in a binary format and should not be edited manually.

The server will also occasionally write ("dump") the complete contents of the updated zone to its zone

ﬁle. This is not done immediately after each dynamic update, because that would be too slow when a

large zone is updated frequently. Instead, the dump is delayed by 15 minutes, allowing additional updates

to take place.

When a server is restarted after a shutdown or crash, it will replay the journal ﬁle to incorporate into the

zone any updates that took place after the last zone dump.

Changes that result from incoming incremental zone transfers are also journalled in a similar way.

The zone ﬁles of dynamic zones cannot normally be edited by hand because they are not guaranteed to

contain the most recent dynamic changes - those are only in the journal ﬁle. The only way to ensure that

the zone ﬁle of a dynamic zone is up to date is to run rndc stop.

If you have to make changes to a dynamic zone manually, the following procedure will work: Shut down

the server using rndc stop (sending a signal or using rndc halt is not sufﬁcient). Wait for the server to

exit, then remove the zone’s .jnl ﬁle, edit the zone ﬁle, and restart the server. Removing the .jnl ﬁle is

necessary because the manual edits will not be present in the journal, rendering it inconsistent with the

contents of the zone ﬁle.