DNS Communication

Gardiner, James James.Gardiner at det.nsw.edu.au
Thu Jan 22 02:31:44 UTC 2009

The slave contacts the master.

In detail:

Master sends a NOTIFY to the slaves (Identified by NS records) The Notify looks much like an SOA query except it has a different Opcode set in the packet header (NOTIFY instead of QUERY).

Upon receipt of the NOTIFY announcement the slave replies with a NOTIFY response (to stop the master sending more NOTIFY announcements).

The slave then proceeds with a normal SOA request just as if the refresh time has counted to 0.
It is a standard UDP port 53 SOA Query, which is answerred with the SOA RSP.

Assuming the serial number in the newly received SOA is greater than the one the slave has, the slave will start a zone transfer (AXFR or IXFR Request).
Note that zone tranfers are done as a TCP (not UDP) port 53 transaction, with the slave as the initiator and the master as the responder. This is because zone transfers do not need to be fast (and they are not, by FTP standards!) but need to be reliable (which they usually are).

Is that what you meant by which protocol?


-----Original Message-----
From: redhat-list-bounces at redhat.com [mailto:redhat-list-bounces at redhat.com] On Behalf Of Giuseppe Fuggiano
Sent: Wednesday, 21 January 2009 7:51 PM
To: General Red Hat Linux discussion list
Subject: Re: DNS Communication

2009/1/21 Gardiner, James <James.Gardiner at det.nsw.edu.au>:
> The NOTIFY message will trigger the slave to send an SOA request to the Master, and an XFER will start if the serial number is higher. In effect it shortcuts the refresh time countdown. This behavior can be turned off with the 'notify no' directive in named.conf.

Specifically, my question is:

Does the slave connect to the master, or viceversa (when either the timeout or a NOTIFY message is triggered)?  Which protocol is used for that connection?

Giuseppe Fuggiano

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