Couple examples of what seems like the DNS resolving correctly:

nslookup github.com
Server:    ::
Address 1: ::

Name:      github.com
Address 1: 192.30.253.112 lb-192-30-253-112-iad.github.com
Address 2: 192.30.253.113 lb-192-30-253-113-iad.github.com

nslookup 192.30.253.113

Server: ::

Address 1: ::

Name: 192.30.253.113

Address 1: 192.30.253.113 lb-192-30-253-113-iad.github.com