DDNS Updates fail When More Than 15 Authoritative Servers (NS records) are listed in a Dynamically Updated Zone

Chris Buxton chris.p.buxton at gmail.com
Mon Sep 20 22:47:48 UTC 2010

It probably has something to do with the packet size. You can't easily fit 25 NS records into a 512 byte UDP packet.

You really don't want to have more than 8 published NS records for most purposes.

Chris Buxton
BlueCat Networks

On Sep 20, 2010, at 2:30 PM, Christopher Cain wrote:

> [I apologize in advance if this is a double post.  I'm not sure if my original went through]
> I was implementing ISC Bind 9.5 at a client site last month and had a single zone that accepted DDNS updates only from the ISC DHCP service.
> The environment consisted of a Master BIND server and almost 25 Windows slave servers.  All DNS servers were listed as authoritative at first.  This caused DDNS updates from DHCP to fail with the following message:
> "Unable to add forward map from host.domain.com to DNS format error".
> After spending quite a bit of time troubleshooting this issue with no luck, I was finally successful with DDNS updates after I reduced the number of authoritative servers for the dynamic zone to 15.  Since I have done this, the issue has not resurface.
> Can anyone help explain to me why this happened and if there is anything I can do to avoid this from happening in the future?
> Thanks,
> Christopher Cain
> E: chris at christophercain.ca
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> bind-users mailing list
> bind-users at lists.isc.org
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