CNAME restrictions

Kevin Darcy kevin.darcy at
Tue Aug 4 20:28:16 UTC 2020

[ Classification Level: GENERAL BUSINESS ]

Offhand, it looks like the server side is configured to only allow
authenticated updates, but you're sending an unauthenticated one.

A more nuanced issue might be if the ID you're running the nsupdate as,
can't read the key files, so even though you may have intended the update
to be signed, it actually wasn't.

Did you try adding a -d to the nsupdate command? If so, does the debug
output give any clues?


On Tue, Aug 4, 2020 at 1:30 PM Leroy Tennison <leroy at>

> I have a situation where, due to the system's location (IP subnet), its
> DNS name is <webserver>.<internal subdomain>  We have a
> certificate for * which we prefer to use instead of
> having to acquire a certificate for <internal subdomain>
> since this is a one-off internal-only web server.  Our (ISC) DNS servers
> (version 9.10.3-P4-Ubuntu that comes with Ubuntu 16.04) serve both
> domains.  I thought a solution would be to use a CNAME but, when I attempt
> this (via nsupdate with the update key which works for A and PTR adds and
> deletes) I get (on "send"):
>  TSIG error with server: expected a TSIG or SIG(0)
> update failed: NOTIMP
> What I tried (on both <internal subdomain> and
> was:
> update add <webserver> 86400 IN CNAME <webserver>.<internal
> subdomain>
> Apparently I'm mis-understanding CNAME usage, if I actually can use a
> CNAME record what should the format be (or do I need to configure bind
> differently to use it since part of the reply is NOTIMP)?  If that's not
> possible due to CNAME restrictions are there any alternatives?
> Thanks for your help.
> Harriscomputer
> *Leroy Tennison*Network Information/Cyber Security Specialist
> E: leroy at
> P:
> 2220 Bush Dr
> McKinney, Texas
> 75070
> <>
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