1) Name server lookup 
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. As of BIND 9.9.0a3, nslookup has apparently been resurrected (`nslookup is no longer to be treated as deprecated`). (The I.....
Name Server Lookup [Unix]