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NETWORKS(5)		    BSD	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, distribu-
     tion 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	li-
     brary, 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 Inter-
     net Assigned Numbers Authority (IANA).

     If	a site changes its ISP from one	to another, it will generally be re-
     quired to change all its assigned IP addresses as part of the conversion;
     that is, return the previous network numbers to the previous ISP, and as-
     sign 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.

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

     getnetent(3), nsswitch.conf(5), resolv.conf(5), hostname(7), dhclient(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.

BSD			       November	17, 2000			   BSD


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