Dig
Basic Usage
dig (domain information groper) gets information from DNS servers.
dig google.com Gets DNS information for the specified hostname.
You can query for specific DNS record types:
dig MX psygen.org Look for the mail exchanger records for the specified hostname.
dig NS psygen.org Look for the name server records for the specified hostname.
... and so on for any valid record type.
Short Form
You can use the short form to view just the info you need, instead of the whole record:
dig psygen.org +short 67.225.240.117
dig psygen.org ns +short ns1.nameserver ns2.nameserver
Reverse DNS Lookup
You can also use dig to do a reverse DNS lookup (find out what domain name an IP address belongs to) (you can remove the "+short" to see the entire record)
dig -x 209.132.183.81 +short www.redhat.com.
Query a Specific DNS Server
By default, dig asks the DNS server that your machine is set to use (usually set by DHCP, and will be your ISP, or company's DNS server.) You can also use dig to ask a specific DNS server to perform the lookup.
dig @ns1.redhat.com redhat.com This will directly ask the redhat name server what the DNS records are for redhat.com
dig @8.8.8.8 redhat.com This will ask Google's public DNS server for the DNS records for redhat.com