- DNS request failed: The name server was unable to process this query due to a problem with the name server.
Nslookup (name server lookup) is a command line tool for querying the domain name system (DNS) servers. It basically query a server on the internet to get a mapping between a given host name and its related IP address. It can also perform reverse lookup (ie: find the name with a given IP address) but reverse records are not mandatory and may not be found within the DNS.
The Internet Systems Consortium has deprecated nslookup in favor of dig. However, nslookup is still widely used by network administrators mainly because of its simplicity.