Google DNS Oddity

Chip Marshall chip at 2bithacker.net
Fri Sep 6 20:40:29 UTC 2019


(Cross posting from NANOG)

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?

Additionally, here's a dig +trace showing the same behavior:

# dig +trace www.google.com. aaaa

; <<>> DiG 9.10.3-P4-Ubuntu <<>> +trace www.google.com. aaaa
;; global options: +cmd
.			40841	IN	NS	b.root-servers.net.
.			40841	IN	NS	g.root-servers.net.
.			40841	IN	NS	k.root-servers.net.
.			40841	IN	NS	i.root-servers.net.
.			40841	IN	NS	m.root-servers.net.
.			40841	IN	NS	c.root-servers.net.
.			40841	IN	NS	l.root-servers.net.
.			40841	IN	NS	e.root-servers.net.
.			40841	IN	NS	d.root-servers.net.
.			40841	IN	NS	f.root-servers.net.
.			40841	IN	NS	h.root-servers.net.
.			40841	IN	NS	j.root-servers.net.
.			40841	IN	NS	a.root-servers.net.
.			40841	IN	RRSIG	NS 8 0 518400 20190917050000 20190904040000 59944 . W93v8sQLROIXL1qvcezKKnL8XwzzxuFb6VbyV7h+SG27BIgJiOGrNE5q M6ncTYozvKd3tKJ/cQZcnIO9zi9tInPKgVctNF1Fp2FGb8TnFuTkIOMy MEVzbWEZrZErcToDRaK1WzlrxBL6gsIfegE8gjC/2XVnKQENZCJ4qgg8 V/u1CKbJGV0nmnVusCZ6pXnkVJDDdvvicaUf0IoxqEONh1h/xKghX14R 6leOUCJpAtdS0M9eyPeBL5myCm7olOVhi/A+9QjZLv60vefYAF7aREtW 5mEvg/YyNz4dUOHrhz/iRbK/wGIbtyuTpvy3Gg/F2dtrVfJBzobDnGpv sFO4xA==
;; Received 525 bytes from 8.8.8.8#53(8.8.8.8) in 1 ms

com.			172800	IN	NS	a.gtld-servers.net.
com.			172800	IN	NS	b.gtld-servers.net.
com.			172800	IN	NS	c.gtld-servers.net.
com.			172800	IN	NS	d.gtld-servers.net.
com.			172800	IN	NS	e.gtld-servers.net.
com.			172800	IN	NS	f.gtld-servers.net.
com.			172800	IN	NS	g.gtld-servers.net.
com.			172800	IN	NS	h.gtld-servers.net.
com.			172800	IN	NS	i.gtld-servers.net.
com.			172800	IN	NS	j.gtld-servers.net.
com.			172800	IN	NS	k.gtld-servers.net.
com.			172800	IN	NS	l.gtld-servers.net.
com.			172800	IN	NS	m.gtld-servers.net.
com.			86400	IN	DS	30909 8 2 E2D3C916F6DEEAC73294E8268FB5885044A833FC5459588F4A9184CF C41A5766
com.			86400	IN	RRSIG	DS 8 1 86400 20190919170000 20190906160000 59944 . ep9gNcyySwR/AqNOnfjXq3OCw5IwOJnIxU4U25UdZ2ejwbJqLf8ytp68 O5DQz1N/PvrEhi1Wg8XyQHZM+fc38cYhhjG5HMVOcEN3wvifnxTWEwBs ay2GxF10TtUpg9TF4Qs2+V8k0ABWwAKIBbSAeZ+C+l5mBg18CCnTgjeg PR+466SgA7sHbzaI9PYK57suhq3uLrphcC2Ti7jmV9V41H5D52gNTiV5 eQ2BsPo+l5LyLrvusailMOzogav9v4M9bnOSGTcc85nf/wD5/Vo4R4MU OexIxio0NGBl7GeS3zoPKV29CYnfcuZBkD2VBuPKZafxp0nIo4olMznn szi9lg==
;; Received 1174 bytes from 199.7.83.42#53(l.root-servers.net) in 60 ms

google.com.		172800	IN	NS	ns2.google.com.
google.com.		172800	IN	NS	ns1.google.com.
google.com.		172800	IN	NS	ns3.google.com.
google.com.		172800	IN	NS	ns4.google.com.
CK0POJMG874LJREF7EFN8430QVIT8BSM.com. 86400 IN NSEC3 1 1 0 - CK0Q1GIN43N1ARRC9OSM6QPQR81H5M9A NS SOA RRSIG DNSKEY NSEC3PARAM
CK0POJMG874LJREF7EFN8430QVIT8BSM.com. 86400 IN RRSIG NSEC3 8 2 86400 20190912044627 20190905033627 17708 com. kXWtAEptQhH9JpsAJzpvEwEwRtybI/FVl9Hrd1lr/GTkZ3P4clnR7YLB quX4CVf8E0+gEfwf4U2PpmphROV1eHweyycVydvTE8etaDipTpItbtyG 7Iz/uKjp1TY3RD+qNa6LZ1juEs70aKPsbmEV79rtiTW2kurdgqslP5jH Jg0=
S84BDVKNH5AGDSI7F5J0O3NPRHU0G7JQ.com. 86400 IN NSEC3 1 1 0 - S84CFH3A62N0FJPC5D9IJ2VJR71OGLV5 NS DS RRSIG
S84BDVKNH5AGDSI7F5J0O3NPRHU0G7JQ.com. 86400 IN RRSIG NSEC3 8 2 86400 20190913045601 20190906034601 17708 com. bJE7LV1REfTtY1jFj/9qA1CKIDBgCJOTV42tSwf92aqhTAkflM9QFH7/ 3Z5440IkZ8PoWMt9Yn7fn+Q+cTZVnbj071jVpiLNXshhMQbtDC1eJkLz AIuATIj+dqWTWQg7vut0oiy0wnJ2ktSgqTFe4JtwRD0lWO6+NgnhbgQD 2yg=
;; Received 776 bytes from 192.43.172.30#53(i.gtld-servers.net) in 74 ms

www-anycast.google.com.	300	IN	AAAA	2001:4860:4802:32::75
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
;; Received 167 bytes from 216.239.38.10#53(ns4.google.com) in 6 ms

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



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