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NETWORKS(5)                   File Formats Manual                  NETWORKS(5)

     networks - Internet Protocol network name data base

     The networks 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 DNS, as controlled by

     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 (DNS) is used instead, except as noted.

     For each IP network a single line should be present with the following
           name network [alias ...]

     These are:
           name     Official network name
           network  IP network number
           alias    Network alias

     Items are separated by any number of blanks and/or tab characters.  A "#"
     indicates the beginning of a comment; 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 inet_network(3) routine from the IP address manipulation
     library, inet(3).  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 their hosts for easy renumbering, to preserve their ability to
     easily change their ISP should the need arise.

     /etc/networks  The networks file resides in /etc.

     getnetent(3), nsswitch.conf(5), resolv.conf(5), hostname(7), dhcpcd(8),
     dhcpd(8), named(8)

     Classless IN-ADDR.ARPA delegation, RFC 2317, March 1998.

     Address Allocation for Private Internets, RFC 1918, February 1996.

     Network 10 Considered Harmful, RFC 1627, July 1994.

     Classless Inter-Domain Routing (CIDR): an Address Assignment and
     Aggregation Strategy, RFC 1519, September 1993.

     DNS Encoding of Network Names and Other Types, RFC 1101, April 1989.

     The networks file format appeared in 4.2BSD.

NetBSD 10.99                     July 14, 2018                    NetBSD 10.99