1.\" $NetBSD: networks.5,v 1.9 1999/03/17 20:19:47 garbled Exp $ 2.\" 3.\" Copyright (c) 1983, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)networks.5 8.1 (Berkeley) 6/5/93 35.\" 36.Dd January 16, 1999 37.Dt NETWORKS 5 38.Os 39.Sh NAME 40.Nm networks 41.Nd Internet Protocol network name data base 42.Sh DESCRIPTION 43The 44.Nm 45file is used as a local source to translate between Internet Protocol 46.Pq Tn IP 47network addresses and network names (and vice versa). 48It can be used in conjunction with the DNS, 49.\"and the 50.\".Tn NIS 51.\"maps 52.\".Sq networks.byaddr , 53.\"and 54.\".Sq networks.byname , 55as controlled by 56.Xr nsswitch.conf 5 . 57.Pp 58While the 59.Nm 60file was originally intended to be an exhaustive list of all 61.Tn IP 62networks that the local host could communicate with, distribution 63and update of such a list for the world-wide 64.Tn Internet 65(or, indeed, for any large "enterprise" network) has proven to be 66prohibitive, so the Domain Name System 67.Pq Tn DNS 68is used instead, except as noted. 69.Pp 70For each 71.Tn IP 72network a single line should be present with the following information: 73.Bd -unfilled -offset indent 74official network name 75ip network number 76aliases 77.Ed 78.Pp 79Items are separated by any number of blanks and/or tab characters. 80A ``#'' indicates the beginning of a comment; characters up to the end of 81the line are not interpreted by routines which search the file. 82.Pp 83Network number may be specified in the conventional 84``.'' (dot) notation using the 85.Xr inet_network 3 86routine 87from the 88.Tn IP 89address manipulation library, 90.Xr inet 3 . 91Network names may contain 92.Qq a 93through 94.Qq z , 95zero through nine, and dash. 96.Pp 97.Tn IP 98network numbers on the 99.Tn Internet 100are generally assigned to a site by its Internet Service Provider 101.Pq Tn ISP , 102who, in turn, get network address space assigned to them by one of 103the regional Internet Registries (e.g. ARIN, RIPE NCC, APNIC). 104These registries, in turn, answer to the Internet Assigned Numbers 105Authority 106.Pq Tn IANA . 107.Pp 108If a site changes its ISP from one to another, it will generally 109be required to change all its assigned IP addresses as part of the 110conversion; that is, return the previous network numbers to the previous 111.Tn ISP , 112and assign addresses to its hosts from 113.Tn IP 114network address space given by the new 115.Tn ISP . 116Thus, it is best for a savvy network manager to configure his 117hosts for easy renumbering, to preserve his ability to easily 118change his 119.Tn ISP 120should the need arise. 121.Sh FILES 122.Bl -tag -width /etc/networks -compact 123.It Pa /etc/networks 124The 125.Nm 126file resides in 127.Pa /etc . 128.El 129.Sh SEE ALSO 130.Xr getnetent 3 , 131.Xr resolv.conf 5 , 132.Xr nsswitch.conf 5 , 133.Xr hostname 7 , 134.Xr dhclient 8 , 135.Xr dhcpd 8 , 136.Xr named 8 , 137.Rs 138.%R RFC 139.%N 2317 140.%D March 1998 141.%T "Classless IN-ADDR.ARPA delegation" 142.Re 143.Rs 144.%R RFC 145.%N 1918 146.%D February 1996 147.%T "Address Allocation for Private Internets" 148.Re 149.Rs 150.%R RFC 151.%N 1627 152.%D July 1994 153.%T "Network 10 Considered Harmful" 154.Re 155.Rs 156.%R RFC 157.%N 1519 158.%D September 1993 159.%T "Classless Inter-Domain Routing (CIDR): an Address Assignment and Aggregation Strategy" 160.Re 161.Rs 162.%R RFC 163.%N 1101 164.%D April 1989 165.%T "DNS Encoding of Network Names and Other Types" 166.Re 167.Sh HISTORY 168The 169.Nm 170file format appeared in 171.Bx 4.2 . 172