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

[Warren Kumari]

On Sun, Jul 6, 2014 at 3:45 PM, Mohamed Lrhazi <ml623 at georgetown.edu> wrote:
> 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....

Nah. No worries. This list traditionally has a wide range of topics.
Your mail was polite and sane, and you seem interested in learning.

Entirely appropriate (IMO) for this list.

W

>
> 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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