nsupdate -g always uses master from SOA to form SPN

Chris Buxton clists at buxtonfamily.us
Thu Aug 26 21:32:42 UTC 2021

Use of a hidden primary makes some sense for external (public) DNS, but IMO not for situations where you would want to use GSS-TSIG. So while I would consider this a bug, I don’t think it will be tripped often.

BIND does support multiple SPNs on a single server, but you have to change how you configure it.

Chris Buxton

> On Aug 26, 2021, at 7:32 AM, Magnus Holmgren <magnus.holmgren at millnet.se> wrote:
> When using GSS-TSIG, nsupdate (with the -g flag) always forms the SPN from the
> master server specified in the SOA record, rather than the server specified
> with the server command. Is that really correct behaviour, or should I report
> this as a bug? I've been scouring the Internet, but couldn't find any prior
> discussion about this particular situation.
> The issue arises when employing a hidden primary, and the server in the SOA
> record is actually a secondary, which I though was a rather common setup. In
> this situation, the real primary has to be specified with the server command,
> and I thought the SPN should represent the service and server being
> communicated with.
> I can work around the problem by adding an SPN matching the SOA primary to
> Kerberos, but AFAIU, BIND can only be configured (tkey-gssapi-credential) to
> use a single SPN to look up keys in the keytab, so all the SPNs involved have
> to be aliases of each other, it seems.
> --
> Magnus Holmgren
> --
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