Redundancy / Dynamic DNS query

Kevin Darcy kcd at
Thu Mar 22 02:29:15 UTC 2001

Sure, you could have some script run the "nsupdate" utility to add and delete
records from that name. See the documentation for nsupdate. Or use the Dynamic
Update features of the Net::DNS Perl module.

But be aware, that unless you set your TTL value very low (which will increase
the traffic on your servers), other nameservers which use cached answers may
still tell their clients to go to "dead" servers even after you update the
address list.

I hope you're not planning to build this mechanism to make an SMTP service more
available; MX records already exist to deal with failover and/or load-balancing
requirements in the SMTP context.

- Kevin

Alistair Nelson wrote:

> Hi,
> If you have a "one name to many ip addresses" configuration with BIND, I
> understand that each time the
> name is accessed BIND will round-robin between the IP addresses, so that
> potentially any server will
> be accessed.
> Is there an easy way (I assume using dynamic DNS) to get DDNS to remove
> unavailable servers, and
> re-add them when they become available?
> For example, if a DNS name called mailhost has three IP address,,
> and
> If the operating system at crashes (for example, fails a ping
> test), DDNS removes
> but then re-adds the address when it becomes available again.
> I apologise if this information is well referenced somewhere, I haven't been
> able to find it. I haven't used DDNS
> yet, but if it can facilitate this functionality then I'd like to learn it.
> Kind regards & thanks in advance for any replies.
> Alistair.

More information about the bind-users mailing list