BIND 8.1.2 Release Notes

New and Changed Features
New Features
Chapter 18
New Features
This section describes the new features in BIND 8.1.2.
Support for DNS Change Notification (RFC 1996)
The DNS NOTIFY operation provides a method for the master server to
inform slave servers that a zone transfer is necessary. In the earlier
versions, slave servers had to poll a master server at an interval of time
as defined in the State of Authority (SOA) record, to check if the serial
number has changed. If a change has occurred, the slave server initiates
a zone transfer. The disadvantage of this approach is that slaves may not
receive new information between the time intervals.
DNS NOTIFY uses a new DNS opcode to notify the slave about a change
in the serial number of the zone’s SOA record. The notification is sent to
all the hosts listed as a name server in NS records for that zone.
Additionally, BIND 8.1.2 allows you to list additional servers to
accommodate stealth servers that may not be listed in any NS records.
You can list these additional servers in the configuration file,
/etc/named.conf, using the zone statement.
When a slave server receives the notify packet, it first sends an
acknowledgment and then behaves as if its refresh timer for that zone
has expired, undergoing the same process used during expiration time
(i.e., first retrieving the SOA record from the master and then initiating
a zone transfer, if the record has changed).
The DNS NOTIFY feature is enabled in the master server by default. In
some environments, the master server in a zone may be an 8.1.2 server
with DNS NOTIFY enabled, while the other servers in the zone may be
4.x servers (without the DNS NOTIFY feature). In such environments,
whenever the master server sends a notification to the other servers, the
4.x servers ignore this notification because they do not understand the
NOTIFY protocol.