Google DNS --- Figuring out which DNS Cluster you are using

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(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 2017).
 This post is being posted with his explicit permission.