why do I get "No response from server"

[Kevin Darcy]

Greg Chavez wrote:
> On 22 Jun 2006 20:35:37 +0100, Chris Thompson <cet1 at hermes.cam.ac.uk> wrote:
>   
>> I am afraid that both my claims were wrong:
>>
>>   that the NS records in the zone were different from the ones
>>   at the delegation point (I had picked the wrong set of NS
>>   records from the authority section of a reply)
>>
>>   that mail1.ccs.bbk.ac.uk was not authoritative for lkl.ac.uk
>>   (its not authoritative for bbk.ac.uk which the CNAME points
>>   into, but so what)
>>
>> That will teach me to post too fast (maybe). Apologies.
>>     
>
> Whenever some name servers cache a RR for a zone positively while
> others cache negatively, the cause always seems to be a TTL issue or a
> lame/dysfunctional delegation.  So, usually follow the same
> troubleshooting process as Mr. Thompson, looking for the bad name
> server.  In fact, *appears* that the mail.ccs.bbk box is to blame.
>
> But its not to blame. It returns the CNAME for www.ilk.ac.uk.
> However, its authority section shows the root servers.  How does that
> happen?  Our Infoblox servers will omit the authority section if
> configured to return minimal responses, but give out the root servers?
>  When I first saw the query response, it looked like an iterative
> brush-off.  Is this broken?  Broken but benign?
>
> ; <<>> DiG 9.2.4 <<>> www.lkl.ac.uk @mail1.ccs.bbk.ac.uk
> ;; global options:  printcmd
> ;; Got answer:
> ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 1848
> ;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 13, ADDITIONAL: 0
>
> ;; QUESTION SECTION:
> ;www.lkl.ac.uk.                 IN      A
>
> ;; ANSWER SECTION:
> www.lkl.ac.uk.          10800   IN      CNAME   thor.dcs.bbk.ac.uk.
>
> ;; AUTHORITY SECTION:
> .                       3600000 IN      NS      J.ROOT-SERVERS.NET.
> .                       3600000 IN      NS      K.ROOT-SERVERS.NET.
> .                       3600000 IN      NS      L.ROOT-SERVERS.NET.
> .                       3600000 IN      NS      M.ROOT-SERVERS.NET.
> .                       3600000 IN      NS      A.ROOT-SERVERS.NET.
> .                       3600000 IN      NS      B.ROOT-SERVERS.NET.
> .                       3600000 IN      NS      C.ROOT-SERVERS.NET.
> .                       3600000 IN      NS      D.ROOT-SERVERS.NET.
> .                       3600000 IN      NS      E.ROOT-SERVERS.NET.
> .                       3600000 IN      NS      F.ROOT-SERVERS.NET.
> .                       3600000 IN      NS      G.ROOT-SERVERS.NET.
> .                       3600000 IN      NS      H.ROOT-SERVERS.NET.
> .                       3600000 IN      NS      I.ROOT-SERVERS.NET.
>
> ;; Query time: 137 msec
> ;; SERVER: 193.61.22.6#53(mail1.ccs.bbk.ac.uk)
> ;; WHEN: Fri Jun 23 08:41:53 2006
> ;; MSG SIZE  rcvd: 269
>   
I'm not sure why you'd consider that "broken" at all. Despite the fact 
that its own name is in a fairly close branch of the namespace 
hierarchy, mail1.ccs.bbk.ac.uk is not considered authoritative for 
thor.dcs.bbk.ac.uk, nor for any domain between that name and the root, 
so if it didn't happen to have anything cached for any of those domain 
levels -- not surprising, since it seems to have recursion completely 
turned off -- the Authority Section of its response should contain, if 
anything, root-zone NSes.

Perhaps you're forgetting that when a CNAME -- or a CNAME chain -- is in 
the Answer Section of a response, the Authority Section applies to the 
target of the CNAME (or the target of the last CNAME in the chain) 
rather than to the QNAME itself.

                                                                         
- Kevin