Google DNS Oddity

Fri Sep 6 19:49:08 UTC 2019

Do you see the same behavior when you execute your dig query without
the trailing dot?

Thanks,
Stephen

> > On Sep 6, 2019, at 3:11 PM, Chip Marshall via NANOG <nanog at nanog.org> wrote:
> > 
> > Hello, I'm seeing an oddity when doing DNS lookups for www.google.com from our
> > London datacenter, and I'm curious if other people are seeing the same
> > behavior.
> > 
> > It appears that when we ask for www.google.com. we sometimes get an answer
> > that only contains records for www-anycast.google.com., which our resolver
> > ignores as they don't match the query.
> > 
> > As seen with dig:
> > 
> > ```
> > # dig @ns1.google.com. www.google.com. aaaa
> > 
> > ; <<>> DiG 9.10.3-P4-Ubuntu <<>> @ns1.google.com. www.google.com. aaaa
> > ; (2 servers found)
> > ;; global options: +cmd
> > ;; Got answer:
> > ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 42641
> > ;; flags: qr aa rd; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1
> > ;; WARNING: recursion requested but not available
> > 
> > ;; OPT PSEUDOSECTION:
> > ; EDNS: version: 0, flags:; udp: 512
> > ;; QUESTION SECTION:
> > ;www.google.com.			IN	AAAA
> > 
> > ;; ANSWER SECTION:
> > www-anycast.google.com.	300	IN	AAAA	2001:4860:4802:34::75
> > www-anycast.google.com.	300	IN	AAAA	2001:4860:4802:38::75
> > www-anycast.google.com.	300	IN	AAAA	2001:4860:4802:36::75
> > www-anycast.google.com.	300	IN	AAAA	2001:4860:4802:32::75
> > 
> > ;; Query time: 7 msec
> > ;; SERVER: 216.239.32.10#53(216.239.32.10)
> > ;; WHEN: Fri Sep 06 19:05:32 UTC 2019
> > ;; MSG SIZE  rcvd: 167
> > ```
> > 
> > So far I've observed this with A and AAAA queries. It's my understanding that
> > without a CNAME record in the answer, the resolver is doing the right thing by
> > ignoring the answer, as there's no linkage between www and www-anycast.
> > 
> > Is this broken, or is this just some weird DNS trick I've not come across
> > before?
>
> You may want to post on dns-operations instead.
>
> Can you do a dig +trace www.google.com instead, that would be more instructive about whatт€™s happening at each layer o
f the delegation.
>
> - Jared