Internet Protocol network name database
file is used as a local source to
translate between Internet Protocol (IP) network addresses and network names
(and vice versa). It can be used in conjunction with the Domain Name System
While the networks
file was originally intended to
be an exhaustive list of all IP networks that the local host could communicate
with, distribution and update of such a list for the world-wide Internet (or,
indeed, for any large "enterprise" network) has proven to be
prohibitive, so the Domain Name System is used instead, except as noted.
For each IP network, a single line should be present with the following
official network name
ip network number
Items are separated by any number of blanks and/or tab characters.
A hash mark (‘
’) indicates the beginning
of a comment; subsequent characters up to the end of the line are not
interpreted by routines which search the file.
Network number may be specified in the conventional
’ (dot) notation using the
routine from the
IP address manipulation library. Network names may contain “a”
through “z”, zero through nine, and dash
IP network numbers on the Internet are generally assigned to a site by its
Internet Service Provider (ISP), who, in turn, get network address space
assigned to them by one of the regional Internet Registries (e.g., ARIN, RIPE
NCC, APNIC). These registries, in turn, answer to the Internet Assigned
Numbers Authority (IANA).
If a site changes its ISP from one to another, it will generally be required to
change all its assigned IP addresses as part of the conversion; that is,
return the previous network numbers to the previous ISP and assign addresses
to its hosts from IP network address space given by the new ISP. Thus, it is
best for a savvy network manager to configure his hosts for easy renumbering,
to preserve his ability to easily change his ISP should the need arise.
DNS Encoding of Network Names and Other Types,
RFC 1101, April 1989.
B. Moskowitz, D. Karrenberg,
G. J. de Groot, and E. Lear,
Address Allocation for Private Internets,
RFC 1918, February
G. de Groot, and P. Vixie,
Classless IN-ADDR.ARPA delegation,
RFC 2317, March 1998.
V. Fuller and
T. Li, Classless Inter-domain
Routing (CIDR): The Internet Address Assignment and Aggregation Plan,
RFC 4632, August
file format appeared in