NODATA type 3 with CNAME

[Barry Margolin]

In article <g70b2b$1ar5$1 at sf1.isc.org>, James Ponder <james at squish.net> 
wrote:

> Hi
> 
> 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.

> 
> $ dig news.bbc.co.uk @212.58.224.21                                         
> ; <<>> DiG 9.3.4-P1.1 <<>> news.bbc.co.uk @212.58.224.21
> ; (1 server found)
> ;; global options:  printcmd
> ;; Got answer:
> ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 12148
> ;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
> 
> ;; QUESTION SECTION:
> ;news.bbc.co.uk.                        IN      A
> 
> ;; ANSWER SECTION:
> news.bbc.co.uk.         3600    IN      CNAME   newswww.bbc.net.uk.
> 
> ;; Query time: 25 msec
> ;; SERVER: 212.58.224.21#53(212.58.224.21)
> ;; WHEN: Sat Aug  2 01:11:13 2008
> ;; MSG SIZE  rcvd: 62
> 
> Thanks
> 
> James

-- 
Barry Margolin, barmar at alum.mit.edu
Arlington, MA
*** PLEASE don't copy me on replies, I'll read them in the group ***