check_dns

[normal]
127.0.0.1
DNS ok - +[\.0-9]+ seconds response time, Address\(es\) is\/are 127\.0\.0\.1

[critical]
$nullhost
DNS (problem - Probably a non-existent host/domain|CRITICAL - Non-existent host/domain|CRITICAL - Connection timed out after [0-9]+ seconds)