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
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 onAugust 23 2017).This post is being posted with his explicit permission.
