Google DNS Oddity

Fri Sep 6 19:11:55 UTC 2019

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?

-- 
Chip Marshall <chip at 2bithacker.net>