[nsd-users] on axfr fallback

[Ondřej Surý]

Shane,

2008/11/13 Shane Kerr <shane at ca.afilias.info>:
> Ondrej,
>
> On Wed, 2008-11-12 at 23:45 +0100, Ondřej Surý wrote:
>> I don't have time to do test, so I am going to ask.  What error code does
>> bind returns if you delete it's journal (and ixfr-from-differences is yes)?
>> Ie. if bind cannot provide IXFR, only AXFR?  Will nsd fallback to AXFR in
>> that case?  (I hope the answer is that it's the FORMATERR error code ;)).
>
> If BIND cannot provide IXFR then it automatically falls back to AXFR.

Alright, you forced me to read RFC1995 ;).

> I think this behavior is badly broken, but it is allowed by the RFC.
> (There are several scenarios which can cause BIND to not have enough
> information to provide IXFR from any particular serial, which means if
> you are unlucky enough to try that server before a server that *can*
> provide IXFR, you have to transfer the entire zone.)

It seems to me, that the problem here is that RFC 1995 tried to be foolproof
and what we really need is:

C: request IXFR
S: return "cannot serve IXFR, try AXFR" error code
C: request AXFR

instead of:

C: request IXFR
S: return IXFR or AXFR

What about making update to RFC1995 to allow server to return error code?

Ondrej
-- 
Ondřej Surý <ondrej at sury.org>