Test if a name server supports EDNS
From Brandonhutchinson.com
Use the following to test if a name server supports EDNS, specifically EDNS0 in the examples below.
When testing a name server, make sure to send a query that will result in authoritative answer. For example, if ns.example.com is authoritative for example.com, send a query such as example.com soa. Sending a query for something like . ns to the name server will result in a timeout when specifying +edns=0.
dig +edns
- If your version of dig supports +edns=#, use the following:
$ dig @nameserver +noall +comments +edns=0 query ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 26316 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 9, ADDITIONAL: 10 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096
dig +bufsize
- If your version of dig does not support +edns=#, you will have to use +bufsize=B.
- According to dig(1), sending a non-zero bufsize causes an EDNS query to be sent.
$ dig @nameserver +noall +comments +bufsize=1 query ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 61334 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 9, ADDITIONAL: 10 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096
