nslookup is a network administration command-line tool available for many computer operating systems for querying the Domain Name System (DNS) to obtain domain name or IP address mapping or for any other specific DNS record.
You can use this tool directly from your own workstation. But, from time to time, you may need to perform an NSLookup from outside your private network. Maybe to verify replication, or maybe to verify someone is who they say they are. This NSLookup tool will help you out.