Why two lookups for a CNAME?

[John Miller]

>>
>> Using dig, I find play.google.com is a CNAME for play.l.google.com.
>>
>>
>> When asked to resolve it, named will first look for play.google.com.  The
>> result
>> will include the CNAME and the IP of the A record.
>>
>>
>> Named then makes a second request to resolve the A record.
>
> Are you sure about this example?
>
> That would be the correct behavior if the target of the CNAME were
> delegated to different servers than the CNAME itself. But both
> google.com and l.google.com are served by ns[1-4].google.com.
>
> You'll see additional queries like this if you look up servers hosted by
> the Akamai CDN, because the CNAME points from the original domain to one
> of Akamai's domains.

Hi Barry,

I just did a double-check (stock RHEL 6 BIND, 9.8.2), and BIND indeed
does do the second lookup for play.l.google.com.  I've attached a pcap
file if anyone's curious.

John

-- 
John Miller
Systems Engineer
Brandeis University
johnmill at brandeis.edu
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