[dns-operations] Why would a recusrive caching server not resolve a CNAME?

[Mohamed Lrhazi]

Thanks Lyle, I did not mean to say that list was defunct, quite the
opposite, I felt that I was a bit spamming it with non global
operational DNS issue....

Yes, I did not debug well, went for the quick fix of clearing the cache....
That being said, end users query for the name and the IPs, always... but
then here they were only getting the CNAME... so am trying to figure out in
what circumstances would that occur... Would a recursive resolver that has
the CNAME in cache, but the A records expired, fail to resolve the A
records, return just the CNAME?

Thanks a lot,
Mohamed.


On Sun, Jul 6, 2014 at 3:13 PM, Lyle Giese <lyle at lcrcomputer.net> wrote:

>  You waited less than an hour before proclaiming the list defunct?  It's
> Sunday in most of the world.  Most of us are doing other things than
> sitting on this list.
>
> That said, my initial thought is that your server answered your question.
> Nothing more.  Did you ask it for the A record for googlemail.l.google.com
> ?  That might have told you more.
>
> Lyle Giese
> LCR Computer Services, Inc.
>
>
> On 07/06/14 13:38, Mohamed Lrhazi wrote:
>
> I am thinking this list is not appropriate for some of my questions...
> Could someone suggest a better one, maybe as active and rich, as this one,
> but more appropriate for general DNS discussions?
>
>  Thanks a lot,
> Mohamed.
>
>
> On Sun, Jul 6, 2014 at 2:02 PM, Mohamed Lrhazi <ml623 at georgetown.edu>
> wrote:
>
>> We had a little mail outage which turned out to be caused by one of our
>> caching DNS servers returning the bellow incomplete reply.
>>
>>  Clearing the cache on the problematic server fixed the issue....
>>
>>  Am thinking it is now impossible for me to find the root cause in this
>> instance... but wondering if you guys could hint at what could cause such a
>> problem... bugs in the DNS servers involved? temporary misconfig at
>> Google's servers? network issue?
>>
>>  The setup is a bit convoluted:
>>
>>  cache server --> resolver cache server --> Internet
>>
>>  The fix was clearing at the first server. so I am guessing at some
>> point the resolver gave the incomplete answer.
>>
>>  Thanks a lot,
>> Mohamed.
>>
>>  ➜  ~  dig mail.google.com @141.161.100.201
>>
>>  ; <<>> DiG 9.9.5-3-Ubuntu <<>> mail.google.com @141.161.100.201
>> ;; global options: +cmd
>> ;; Got answer:
>> ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 20414
>> ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 4, ADDITIONAL: 5
>>
>>  ;; OPT PSEUDOSECTION:
>> ; EDNS: version: 0, flags:; udp: 4096
>> ;; QUESTION SECTION:
>> ;mail.google.com. IN A
>>
>>  ;; ANSWER SECTION:
>> mail.google.com. 10213 IN CNAME googlemail.l.google.com.
>>
>>  ;; AUTHORITY SECTION:
>> google.com. 96485 IN NS ns2.google.com.
>> google.com. 96485 IN NS ns3.google.com.
>> google.com. 96485 IN NS ns4.google.com.
>> google.com. 96485 IN NS ns1.google.com.
>>
>>  ;; ADDITIONAL SECTION:
>> ns3.google.com. 108462 IN A 216.239.36.10
>> ns4.google.com. 108462 IN A 216.239.38.10
>> ns1.google.com. 108462 IN A 216.239.32.10
>> ns2.google.com. 108462 IN A 216.239.34.10
>>
>>  ;; Query time: 22 msec
>> ;; SERVER: 141.161.100.201#53(141.161.100.201)
>> ;; WHEN: Sun Jul 06 12:42:09 EDT 2014
>> ;; MSG SIZE  rcvd: 207
>>
>>
>>
>
>
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