NODATA type 3 with CNAME

[James Ponder]

On Fri, Aug 01, 2008 at 11:54:09PM -0400, Barry Margolin wrote:
> > Can someone clarify for me the section in RFC 2308 on type 3 NODATA
> > responses when there is a CNAME?
> > 
> > The RFC shows an example where the response is a NOERROR with 0 answers,
> > 0 authorities and 0 additionals, indicating that this is a type 3 NODATA
> > response, and then goes on to say that a CNAME could also be included,
> > "in which case it would be the value of the last CNAME for which NODATA
> > would be concluded."
> > 
> > The reason for my question is that all 4 of the authoritative
> > nameservers for news.bbc.co.uk respond with what looks to me like a type
> > 3 NODATA response, but clearly news.bbc.co.uk is very popular and works
> > well.
> 
> What's the problem?  The server is authoritative for the bbc.co.uk 
> domain, but not for bbc.net.uk, and has recursion disabled, so it can't 
> resolve the CNAME.  The client nameserver restarts its query using the 
> target of the CNAME.

I guess perhaps the problem is RFC 2308 was written in the days before
bailiwick checks.

So, would you say the correct algorithm to detect a NODATA in this
situation is to check if the value of the last CNAME is in-bailiwick or
not?  If it's in-bailiwick then it's a type 3 NODATA, if it's outside
then the nameserver will restart the query with the traget?

Likewise, in the case of
  bailiwick bbc.co.uk, NOERROR, 2 ans, 0 auth, 0 add
  lookup news.bbc.co.uk type A
Answer 1: news.bbc.co.uk CNAME something.else
Answer 2: something.else CNAME news2.bbc.co.uk

Would I be correct in saying a resolver should not accept this as a type
3 NODATA and should ignore the out-of-bailiwick second CNAME, and
restart using the target of the first CNAME?

Thanks for your help.

James