Google DNS --- Figuring out which DNS Cluster you are using
Alejandro Acosta
R+D Coordinator
(this is -almost- a copy / paste of an email sent by Erik Sundberg to nanog mailing list on August 23). This post is being posted with his explicit permission.
I sent this out on the outage list, with a lots of good feedback sent to me. So I figured it would be useful to share the information on nanog as well.
A couple months ago had to troubleshoot a google DNS issue with Google’s NOC. Below is some helpful information on how to determine which DNS Cluster you are going to.
Let’s remember that Google runs DNS Anycast for DNS queries to 8.8.8.8 and 8.8.4.4. Anycast routes your DNS queries to the closes DNS cluster based on the best route / lowest metric to 8.8.8.8/8.8.4.4. Google has deployed multiple DNS clusters across the world and each DNS Cluster has multiple servers.
So a DNS query in Chicago will go to a different DNS clusters than queries from a device in Atlanta or New York.
How to get a list of google DNS Cluster’s
# dig -t TXT +short locations.publicdns.goog. @8.8.8.8
How to print this list in a table format. Script from: https://developers.google.com/speed/public-dns/faq
---------------
#!/bin/bash
IFS="\"$IFS"
for LOC in $(dig -t TXT +short locations.publicdns.goog. @8.8.8.8)
do
case $LOC in
'') : ;;
*.*|*:*) printf '%s ' ${LOC} ;;
*) printf '%s\n' ${LOC} ;;
esac
done
---------------
Which will give you a list like below. This is all of the IP network’s that google uses for their DNS Clusters and their associated locations.
74.125.18.0/26 iad
74.125.18.64/26 iad
74.125.18.128/26 syd
74.125.18.192/26 lhr
74.125.19.0/24 mrn
74.125.41.0/24 tpe
74.125.42.0/24 atl
74.125.44.0/24 mrn
74.125.45.0/24 tul
74.125.46.0/24 lpp
74.125.47.0/24 bru
74.125.72.0/24 cbf
74.125.73.0/24 bru
74.125.74.0/24 lpp
74.125.75.0/24 chs
74.125.76.0/24 cbf
74.125.77.0/24 chs
74.125.79.0/24 lpp
74.125.80.0/24 dls
74.125.81.0/24 dub
74.125.92.0/24 mrn
74.125.93.0/24 cbf
74.125.112.0/24 lpp
74.125.113.0/24 cbf
74.125.115.0/24 tul
74.125.176.0/24 mrn
74.125.177.0/24 atl
74.125.179.0/24 cbf
74.125.181.0/24 bru
74.125.182.0/24 cbf
74.125.183.0/24 cbf
74.125.184.0/24 chs
74.125.186.0/24 dls
74.125.187.0/24 dls
74.125.190.0/24 sin
74.125.191.0/24 tul
172.217.32.0/26 lhr
172.217.32.64/26 lhr
172.217.32.128/26 sin
172.217.33.0/26 syd
172.217.33.64/26 syd
172.217.33.128/26 fra
172.217.33.192/26 fra
172.217.34.0/26 fra
172.217.34.64/26 bom
172.217.34.192/26 bom
172.217.35.0/24 gru
172.217.36.0/24 atl
172.217.37.0/24 gru
173.194.90.0/24 cbf
173.194.91.0/24 scl
173.194.93.0/24 tpe
173.194.94.0/24 cbf
173.194.95.0/24 tul
173.194.97.0/24 chs
173.194.98.0/24 lpp
173.194.99.0/24 tul
173.194.100.0/24 mrn
173.194.101.0/24 tul
173.194.102.0/24 atl
173.194.103.0/24 cbf
173.194.168.0/26 nrt
173.194.168.64/26 nrt
173.194.168.128/26 nrt
173.194.168.192/26 iad
173.194.169.0/24 grq
173.194.170.0/24 grq
173.194.171.0/24 tpe
2404:6800:4000::/48 bom
2404:6800:4003::/48 sin
2404:6800:4006::/48 syd
2404:6800:4008::/48 tpe
2404:6800:400b::/48 nrt
2607:f8b0:4001::/48 cbf
2607:f8b0:4002::/48 atl
2607:f8b0:4003::/48 tul
2607:f8b0:4004::/48 iad
2607:f8b0:400c::/48 chs
2607:f8b0:400d::/48 mrn
2607:f8b0:400e::/48 dls
2800:3f0:4001::/48 gru
2800:3f0:4003::/48 scl
2a00:1450:4001::/48 fra
2a00:1450:4009::/48 lhr
2a00:1450:400b::/48 dub
2a00:1450:400c::/48 bru
2a00:1450:4010::/48 lpp
2a00:1450:4013::/48 grq
There are
IPv4 Networks: 68
IPv6 Networks: 20
DNS Cluster’s Identified by POP Code’s: 20
DNS Clusters identified by POP Code to City, State, or Country. Not all of these are Google’s Core Datacenters, some of them are Edge Points of Presences (POPs). https://peering.google.com/#/infrastructure and https://www.google.com/about/datacenters/inside/locations/
Most of these are airport codes, it did my best to get the location correct:
iad Washington, DC
syd Sydney, Australia
lhr London, UK
mrn Lenoir, NC
tpe Taiwan
atl Altanta, GA
tul Tulsa, OK
lpp Findland
bru Brussels, Belgium
cbf Council Bluffs, IA
chs Charleston, SC
dls The Dalles, Oregon
dub Dublin, Ireland
sin Singapore
fra Frankfort, Germany
bom Mumbai, India
gru Sao Paulo, Brazil
scl Santiago, Chile
nrt Tokyo, Japan
grq Groningen, Netherlans
Which Google DNS Server Cluster am I using. I am testing this from Chicago, IL
# dig o-o.myaddr.l.google.com -t txt +short @8.8.8.8
"173.194.94.135" <<<<<<DNS Server IP, reference the list above to get the cluster, Council Bluffs, IA
"edns0-client-subnet 207.xxx.xxx.0/24" <<<< Your Source IP Block
Side note, the google dns servers will not respond to DNS queries to the Cluster’s Member’s IP, they will only respond to dns queries to 8.8.8.8 and 8.8.4.4. So the following will not work.
dig google.com @173.194.94.135
Now to see the DNS Cluster load balancing in action. I am doing a dig query from our Telx\Digital Realty POP in Atlanta, GA. We do peer with google at this location.
I dig a dig query about 10 times and received the following unique dns cluster member ip’s as responses.
dig o-o.myaddr.l.google.com -t txt +short @8.8.8.8
"74.125.42.138"
"173.194.102.132"
"74.125.177.5"
"74.125.177.74"
"74.125.177.71"
"74.125.177.4"
Which all are Google DNS Networks in Atlanta.
74.125.42.0/24 atl
74.125.177.0/24 atl
172.217.36.0/24 atl
173.194.102.0/24 atl
2607:f8b0:4002::/48 atl
Just thought it would be helpful when troubleshooting google DNS issues.
(this is -almost- a copy / paste of an email sent by Erik Sundberg to nanog mailing list on August 23). This post is being posted with his explicit permission.