HP-UX IP Address and Client Management Administrator's Guide HP-UX 11i v2, HP-UX 11i v3

whenever the master changes and sends a notification to other servers, the 4.x servers ignore
this notification because they do not understand the DNS Notify protocol.
Dynamic DNS Update
Dynamic DNS update is the ability to add, modify, or delete resource records in the master zone
files under a specified zone. Dynamic update is based on RFC 2136 (Dynamic Updates in the
Domain Name System (DNS UPDATE)). Resource records provide a set of information about
each of the domain names. You can enable dynamic update on a zone-by-zone basis by including
an allow-update or update-policy clause in the zone statement.
Using this feature, you can add or remove resource records from a zone without manually editing
the zone file. Do not edit the zone files manually because the zone files on the disk at any given
time may not contain the latest changes performed by other dynamic updates. A single update
request can contain requests to add or remove more than one resource record. You can use the
nsupdate utility to submit dynamic DNS update requests to a name server. For more information
on using this tool, type man 1 nsupdate at the command prompt.
Incremental Zone Transfer
The Incremental Zone Transfer Protocol (IXFR) is a mechanism for slave servers to transfer only
the changed data, instead of transferring the entire zone data every time the zone data changes.
This is defined in RFC 1995.
During a dynamic update and the NOTIFY announcement, the zones are updated according to
the changes in the network, and these changes are immediately propagated to all the authoritative
name servers for the zones. Each time the master server receives an update that increments the
zone’s serial number, the master server sends a NOTIFY announcement to its slaves. And each
time the slaves receive NOTIFY announcements, they check the serial number of the zone on
their master server and transfer the zone. If the zone is large, the transfer can take a considerable
amount of time, within which another update may arrive. As a result, the slave servers transfer
the zone contents continuously, and the name servers spend more time transferring the entire
zone even when the change to the zone is minor.
Incremental zone transfer solves this problem by allowing slave name servers to inform their
master servers about the version of a zone they currently hold, and to request just the changes
to the zone between that version and the current version. This reduces the size and duration of
a zone transfer.
While acting as a master, BIND supports IXFR for the zones where the change history information
is available. These include master zones maintained by dynamic updates and slave zones whose
data was obtained by IXFR. BIND does not support incremental zone transfer for master zones
maintained manually, or for slave zones obtained by an AXFR (the type of query that initiates
a full zone transfer).
When acting as a slave, BIND attempts to use IXFR unless incremental zone transfer is explicitly
disabled.
The option statements used to enable and disable IXFR are:
[provide-ixfr
yes_or_no;]
[request-ixfr
yes_or_no;]
You can set these options manually in the /etc/named.conf configuration file to yes or no
to enable or disable the incremental zone transfer.
The provide-ixfr clause determines whether the local server, acting as a master, responds
with an incremental zone transfer when the given remote server (a slave) requests a zone transfer.
If set to yes, incremental transfer is provided whenever possible. If set to no, all transfers to the
remote server are non-incremental. If this clause is not set, the value of the provide-ixfr
option in the global options block is used as the default.
18 Overview