Using the @dnsp.co resolver:

The dnsp.co resolver will answer with a fixed result: either 123.45.67.89 for an IPv4 A request or 1111:2222:3333:4444:5555:6666:7777:8888 for an IPv6 AAAA request. If you query, for instance, for "www.google.com" and get an answer different from those it means that somewhere along the line the response has been modified.


In addition, since the resolver will answer for absolutely anything (including anything you just make up) you can use it to test to make sure that resolving is happening with something that is guaranteed not to be cached somehow by your local system.


Syntax:

dig @dnsp.co www.example.org
nslookup www.example.org dnsp.co
host www.example.org dnsp.co

Examples:

prompt> dig A @dnsp.co www.google.com ; <<>> DiG 9.8.3-P1 <<>> @dnsp.co www.google.com ; (2 servers found) ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 13495 ;; flags: qr aa ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;www.google.com. IN A ;; ANSWER SECTION: www.google.com. 0 IN A 123.45.67.89 ;; Query time: 32 msec ;; SERVER: 192.155.94.246#53(192.155.94.246) ;; WHEN: Sun Dec 21 19:38:15 2014 ;; MSG SIZE rcvd: 48
prompt> dig AAAA @dnsp.co www.google.com ; <<>> DiG 9.8.3-P1 <<>> AAAA @dnsp.co www.google.com ; (2 servers found) ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 44530 ;; flags: qr aa ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;www.google.com. IN AAAA ;; ANSWER SECTION: www.google.com. 0 IN AAAA 1111:2222:3333:4444:5555:6666:7777:8888 ;; Query time: 37 msec ;; SERVER: 192.155.94.246#53(192.155.94.246) ;; WHEN: Sun Dec 21 19:38:16 2014 ;; MSG SIZE rcvd: 60