1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" From: @(#)inet.4 8.1 (Berkeley) 6/5/93 33.\" $FreeBSD: src/share/man/man4/inet.4,v 1.11.2.6 2001/12/17 11:30:12 ru Exp $ 34.\" $DragonFly: src/share/man/man4/inet.4,v 1.2 2003/06/17 04:36:59 dillon Exp $ 35.\" 36.Dd February 14, 1995 37.Dt INET 4 38.Os 39.Sh NAME 40.Nm inet 41.Nd Internet protocol family 42.Sh SYNOPSIS 43.In sys/types.h 44.In netinet/in.h 45.Sh DESCRIPTION 46The Internet protocol family is a collection of protocols 47layered atop the 48.Em Internet Protocol 49.Pq Tn IP 50transport layer, and utilizing the Internet address format. 51The Internet family provides protocol support for the 52.Dv SOCK_STREAM , SOCK_DGRAM , 53and 54.Dv SOCK_RAW 55socket types; the 56.Dv SOCK_RAW 57interface provides access to the 58.Tn IP 59protocol. 60.Sh ADDRESSING 61Internet addresses are four byte quantities, stored in 62network standard format (on the 63.Tn VAX 64these are word and byte 65reversed). The include file 66.Aq Pa netinet/in.h 67defines this address 68as a discriminated union. 69.Pp 70Sockets bound to the Internet protocol family utilize 71the following addressing structure, 72.Bd -literal -offset indent 73struct sockaddr_in { 74 u_char sin_len; 75 u_char sin_family; 76 u_short sin_port; 77 struct in_addr sin_addr; 78 char sin_zero[8]; 79}; 80.Ed 81.Pp 82Sockets may be created with the local address 83.Dv INADDR_ANY 84to affect 85.Dq wildcard 86matching on incoming messages. 87The address in a 88.Xr connect 2 89or 90.Xr sendto 2 91call may be given as 92.Dv INADDR_ANY 93to mean 94.Dq this host . 95The distinguished address 96.Dv INADDR_BROADCAST 97is allowed as a shorthand for the broadcast address on the primary 98network if the first network configured supports broadcast. 99.Sh PROTOCOLS 100The Internet protocol family is comprised of 101the 102.Tn IP 103network protocol, Internet Control 104Message Protocol 105.Pq Tn ICMP , 106Internet Group Management Protocol 107.Pq Tn IGMP , 108Transmission Control 109Protocol 110.Pq Tn TCP , 111and User Datagram Protocol 112.Pq Tn UDP . 113.Tn TCP 114is used to support the 115.Dv SOCK_STREAM 116abstraction while 117.Tn UDP 118is used to support the 119.Dv SOCK_DGRAM 120abstraction. A raw interface to 121.Tn IP 122is available 123by creating an Internet socket of type 124.Dv SOCK_RAW . 125The 126.Tn ICMP 127message protocol is accessible from a raw socket. 128.Pp 129The 32-bit Internet address contains both network and host parts. 130However, direct examination of addresses is discouraged. For those 131programs which absolutely need to break addresses into their component 132parts, the following 133.Xr ioctl 2 134commands are provided for a datagram socket in the Internet domain; 135they have the same form as the 136.Dv SIOCIFADDR 137command (see 138.Xr intro 4 ) . 139.Pp 140.Bl -tag -width SIOCSIFNETMASK 141.It Dv SIOCSIFNETMASK 142Set interface network mask. 143The network mask defines the network part of the address; 144if it contains more of the address than the address type would indicate, 145then subnets are in use. 146.It Dv SIOCGIFNETMASK 147Get interface network mask. 148.El 149.Sh ROUTING 150The current implementation of Internet protocols includes some routing-table 151adaptations to provide enhanced caching of certain end-to-end 152information necessary for Transaction TCP and Path MTU Discovery. The 153following changes are the most significant: 154.Bl -enum 155.It 156All IP routes, except those with the 157.Dv RTF_CLONING 158flag and those to multicast destinations, have the 159.Dv RTF_PRCLONING 160flag forcibly enabled (they are thus said to be 161.Dq "protocol cloning" ) . 162.It 163When the last reference to an IP route is dropped, the route is 164examined to determine if it was created by cloning such a route. If 165this is the case, the 166.Dv RTF_PROTO3 167flag is turned on, and the expiration timer is initialized to go off 168in net.inet.ip.rtexpire seconds. If such a route is re-referenced, 169the flag and expiration timer are reset. 170.It 171A kernel timeout runs once every ten minutes, or sooner if there are 172soon-to-expire routes in the kernel routing table, and deletes the 173expired routes. 174.El 175.Pp 176A dynamic process is in place to modify the value of 177net.inet.ip.rtexpire if the number of cached routes grows too large. 178If after an expiration run there are still more than 179net.inet.ip.rtmaxcache unreferenced routes remaining, the rtexpire 180value is multiplied by 3/4, and any routes which have longer 181expiration times have those times adjusted. This process is damped 182somewhat by specification of a minimum rtexpire value 183(net.inet.ip.rtminexpire), and by restricting the reduction to once in 184a ten-minute period. 185.Pp 186If some external process deletes the original route from which a 187protocol-cloned route was generated, the ``child route'' is deleted. 188(This is actually a generic mechanism in the routing code support for 189protocol-requested cloning.) 190.Pp 191No attempt is made to manage routes which were not created by protocol 192cloning; these are assumed to be static, under the management of an 193external routing process, or under the management of a link layer 194(e.g., 195.Tn ARP 196for Ethernets). 197.Pp 198Only certain types of network activity will result in the cloning of a 199route using this mechanism. Specifically, those protocols (such as 200.Tn TCP 201and 202.Tn UDP ) 203which themselves cache a long-lasting reference to route for a destination 204will trigger the mechanism; whereas raw 205.Tn IP 206packets, whether locally-generated or forwarded, will not. 207.Ss MIB Variables 208A number of variables are implemented in the net.inet branch of the 209.Xr sysctl 3 210MIB. 211In addition to the variables supported by the transport protocols 212(for which the respective manual pages may be consulted), 213the following general variables are defined: 214.Bl -tag -width IPCTL_FASTFORWARDING 215.It Dv IPCTL_FORWARDING 216.Pq ip.forwarding 217Boolean: enable/disable forwarding of IP packets. 218Defaults to off. 219.It Dv IPCTL_FASTFORWARDING 220.Pq ip.fastforwarding 221Boolean: enable/disable the use of fast IP forwarding code. 222Defaults to off. 223When fast forwarding is enabled, IP packets are forwarded directly to 224the appropriate network interface with a minimal validity checking, which 225greatly improves the throughput. On the other hand, they bypass the 226standard procedures, such as IP option processing and 227.Xr ipfirewall 4 228checking. 229It is not guaranteed that every packet will be fast-forwarded. 230.It Dv IPCTL_SENDREDIRECTS 231.Pq ip.redirect 232Boolean: enable/disable sending of ICMP redirects in response to 233unforwardable 234.Tn IP 235packets. 236Defaults to on. 237.It Dv IPCTL_DEFTTL 238.Pq ip.ttl 239Integer: default time-to-live 240.Pq Dq TTL 241to use for outgoing 242.Tn IP 243packets. 244.It Dv IPCTL_SOURCEROUTE 245.Pq ip.sourceroute 246Boolean: enable/disable forwarding of source-routed IP packets (default false). 247.It Dv IPCTL_RTEXPIRE 248.Pq ip.rtexpire 249Integer: lifetime in seconds of protocol-cloned 250.Tn IP 251routes after the last reference drops (default one hour). This value 252varies dynamically as described above. 253.It Dv IPCTL_RTMINEXPIRE 254.Pq ip.rtminexpire 255Integer: minimum value of ip.rtexpire (default ten seconds). This 256value has no effect on user modifications, but restricts the dynamic 257adaptation described above. 258.It Dv IPCTL_RTMAXCACHE 259.Pq ip.rtmaxcache 260Integer: trigger level of cached, unreferenced, protocol-cloned routes 261which initiates dynamic adaptation (default 128). 262.El 263.Sh SEE ALSO 264.Xr ioctl 2 , 265.Xr socket 2 , 266.Xr sysctl 3 , 267.Xr icmp 4 , 268.Xr intro 4 , 269.Xr ip 4 , 270.Xr ipfirewall 4 , 271.Xr tcp 4 , 272.Xr ttcp 4 , 273.Xr udp 4 274.Rs 275.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 276.%B PS1 277.%N 7 278.Re 279.Rs 280.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 281.%B PS1 282.%N 8 283.Re 284.Sh CAVEAT 285The Internet protocol support is subject to change as 286the Internet protocols develop. Users should not depend 287on details of the current implementation, but rather 288the services exported. 289.Sh HISTORY 290The 291.Nm 292protocol interface appeared in 293.Bx 4.2 . 294The 295.Dq protocol cloning 296code appeared in 297.Fx 2.1 . 298