EDNS support by Google's Public DNS

13-04-2015

Just was looking around at EDNS support by Google. To find how it supports and how packet looks like I created a test NS records for dnstest.anuragbhatia.com pointing to one of test server (178.238.225.247). I wasn’t running any DNS server on the server. Just ran quick tcpdump.

At server end:

sudo tcpdump 'port 53 and dst 178.238.225.247' -nn -vvv -w sample.pcap

Then I forcefully triggered DNS queries via Google’s recursor using:**

dig @8.8.8.8 dnstest.anuragbhatia.com

At server end dump was captured. In wireshark came across the packet:

Packet dump > DNS Query > Addition records > Type OPT > Option C Subnet - Client Subnet this shows client subnet of BSNL from which I queried. :)

This is a very important project pushed by Google, OpenDNS etc to help CDNs (which are based on DNS resolution) perform optimally when end users use non-ISP based recursors. You can read more about project here.