1.\" $OpenBSD: inet.4,v 1.20 2019/10/30 10:39:53 jmc Exp $ 2.\" $NetBSD: inet.4,v 1.3 1994/11/30 16:22:18 jtc Exp $ 3.\" 4.\" Copyright (c) 1983, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)inet.4 8.1 (Berkeley) 6/5/93 32.\" 33.Dd $Mdocdate: October 30 2019 $ 34.Dt INET 4 35.Os 36.Sh NAME 37.Nm inet 38.Nd Internet protocol family 39.Sh SYNOPSIS 40.In sys/types.h 41.In netinet/in.h 42.Sh DESCRIPTION 43The Internet protocol family is a collection of protocols 44layered atop the 45.Em Internet Protocol 46.Pq Tn IP 47transport layer, and utilizing the Internet address format. 48The Internet family provides protocol support for the 49.Dv SOCK_STREAM , 50.Dv SOCK_DGRAM , 51and 52.Dv SOCK_RAW 53socket types; the 54.Dv SOCK_RAW 55interface provides access to the 56.Tn IP 57protocol. 58.Sh ADDRESSING 59Internet addresses are four byte quantities, stored in 60network standard format. 61The include file 62.In netinet/in.h 63defines this address as a discriminated union. 64.Pp 65Sockets bound to the Internet protocol family utilize 66the following addressing structure, 67.Bd -literal -offset indent 68struct sockaddr_in { 69 u_int8_t sin_len; 70 sa_family_t sin_family; 71 in_port_t sin_port; 72 struct in_addr sin_addr; 73 int8_t sin_zero[8]; 74}; 75.Ed 76.Pp 77Sockets may be created with the local address 78.Dv INADDR_ANY 79to effect 80.Dq wildcard 81matching on incoming messages. 82The address in a 83.Xr connect 2 84or 85.Xr sendto 2 86call may be given as 87.Dv INADDR_ANY 88to mean 89.Dq this host . 90The distinguished address 91.Dv INADDR_BROADCAST 92is allowed as a shorthand for the broadcast address on the primary 93network if the first network configured supports broadcast. 94.Sh PROTOCOLS 95The Internet protocol family is comprised of 96the 97.Tn IP 98transport protocol, Internet Control 99Message Protocol 100.Pq Tn ICMP , 101Transmission Control 102Protocol 103.Pq Tn TCP , 104and User Datagram Protocol 105.Pq Tn UDP . 106.Tn TCP 107is used to support the 108.Dv SOCK_STREAM 109abstraction while 110.Tn UDP 111is used to support the 112.Dv SOCK_DGRAM 113abstraction. 114A raw interface to 115.Tn IP 116is available 117by creating an Internet socket of type 118.Dv SOCK_RAW . 119The 120.Tn ICMP 121message protocol is accessible from a raw socket. 122.Pp 123The 32-bit Internet address contains both network and host parts. 124It is frequency-encoded; the most-significant bit is clear 125in Class A addresses, in which the high-order 8 bits are the network 126number. 127Class B addresses use the high-order 16 bits as the network field, 128and Class C addresses have a 24-bit network part. 129Sites with a cluster of local networks and a connection to the 130Internet may choose to use a single network number for the cluster; 131this is done by using subnet addressing. 132The local (host) portion of the address is further subdivided 133into subnet and host parts. 134Within a subnet, each subnet appears to be an individual network; 135externally, the entire cluster appears to be a single, uniform 136network requiring only a single routing entry. 137Subnet addressing is enabled and examined by the following 138.Xr ioctl 2 139commands on a datagram socket in the Internet domain; 140they have the same form as the 141.Dv SIOCIFADDR 142command (see 143.Xr netintro 4 ) . 144.Bl -tag -width SIOCSIFNETMASK 145.It Dv SIOCSIFNETMASK 146Set interface network mask. 147The network mask defines the network part of the address; 148if it contains more of the address than the address type would indicate, 149then subnets are in use. 150.It Dv SIOCGIFNETMASK 151Get interface network mask. 152.El 153.Sh SEE ALSO 154.Xr ioctl 2 , 155.Xr socket 2 , 156.Xr inet_net_ntop 3 , 157.Xr inet_ntop 3 , 158.Xr icmp 4 , 159.Xr ip 4 , 160.Xr netintro 4 , 161.Xr tcp 4 , 162.Xr udp 4 163.Rs 164.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 165.%B PS1 166.%N 7 167.Re 168.Rs 169.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 170.%B PS1 171.%N 8 172.Re 173.Sh HISTORY 174The 175.Nm 176protocol interface appeared in 177.Bx 4.2 . 178.Sh CAVEATS 179The Internet protocol support is subject to change as 180the Internet protocols develop. 181Users should not depend on details of the current implementation, but rather 182the services exported. 183