From RFC 1918

Un-routabe domains

The Internet Assigned Numbers Authority (IANA) has
reserved the following three blocks of the IP address
space for private internets:

IPUpper LimitNote
10.0.0.010.255.255.255(10/8 prefix)
127.0.0.0127.255.255.25510/8 prefix)
169.254.0.0169.254.255.255as of July 2001
172.16.0.0172.31.255.255(172.16/12 prefix)
192.168.0.0192.168.255.255(192.168/16 prefix)

And 127.0.0.1

Information provided by:
Jason Beens, KB0CDN
                and
Ken Cuddeback,NT7K