networks - Internet Protocol network name database
The networks file is used as a local source to translate between Internet
Protocol (IP) network addresses and network names (and vice
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
and update of such a list for the world-wide Internet
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
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 `.'
using the inet_network(3) routine from the IP address manipulation library,
inet(3). Network names may contain "a" through "z",
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
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
hosts for easy renumbering, to preserve his ability to easily change his
ISP should the need arise.
getnetent(3), resolver(3), resolv.conf(5), hostname(7),
Classless IN-ADDR.ARPA delegation, RFC 2317, March 1998.
Address Allocation for Private Internets, RFC 1918, February
Network 10 Considered Harmful, RFC 1627, July 1994.
Classless Inter-Domain Routing (CIDR): an Address Assignment
Aggregation Strategy, RFC 1519, September 1993.
DNS Encoding of Network Names and Other Types, RFC 1101,
The networks file format appeared in 4.2BSD.
OpenBSD 3.6 June 5, 1993
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