whois, nslookup, ping

whois

The whois command will get domain registration information about a Web site. Usage:

whois example.com

nslookup

Used to query nameservers. You can find out a site's IP address with this command.

$ nslookup google.com
Server:         66.94.25.120
Address:        66.94.25.120#53

Non-authoritative answer:
Name:   google.com
Address: 64.233.187.99
Name:   google.com
Address: 64.233.167.99
Name:   google.com
Address: 72.14.207.99

ping

Ping a site to see if you get a response. It will also tell you the remote site's IP address.

$ ping google.com
PING google.com (64.233.187.99) 56(84) bytes of data.
64 bytes from jc-in-f99.google.com (64.233.187.99): icmp_seq=1 ttl=242 time=33.0 ms
64 bytes from jc-in-f99.google.com (64.233.187.99): icmp_seq=2 ttl=242 time=31.8 ms
64 bytes from jc-in-f99.google.com (64.233.187.99): icmp_seq=3 ttl=242 time=44.2 ms
64 bytes from jc-in-f99.google.com (64.233.187.99): icmp_seq=4 ttl=242 time=29.7 ms
64 bytes from jc-in-f99.google.com (64.233.187.99): icmp_seq=5 ttl=242 time=52.0 ms
64 bytes from jc-in-f99.google.com (64.233.187.99): icmp_seq=6 ttl=242 time=46.8 ms
64 bytes from jc-in-f99.google.com (64.233.187.99): icmp_seq=7 ttl=242 time=48.8 ms
64 bytes from jc-in-f99.google.com (64.233.187.99): icmp_seq=8 ttl=242 time=55.3 ms
64 bytes from jc-in-f99.google.com (64.233.187.99): icmp_seq=9 ttl=242 time=43.4 ms