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.\" $FreeBSD$ 34.\" 35.Dd April 9, 2005 36.Dt INET 4 37.Os 38.Sh NAME 39.Nm inet 40.Nd Internet protocol family 41.Sh SYNOPSIS 42.In sys/types.h 43.In netinet/in.h 44.Sh DESCRIPTION 45The Internet protocol family is a collection of protocols 46layered atop the 47.Em Internet Protocol 48.Pq Tn IP 49transport layer, and utilizing the Internet address format. 50The Internet family provides protocol support for the 51.Dv SOCK_STREAM , SOCK_DGRAM , 52and 53.Dv SOCK_RAW 54socket types; the 55.Dv SOCK_RAW 56interface provides access to the 57.Tn IP 58protocol. 59.Sh ADDRESSING 60Internet addresses are four byte quantities, stored in 61network standard format (on little endian machines, such as the 62.Tn alpha , 63.Tn amd64 , 64.Tn i386 65and 66.Tn ia64 67these are word and byte reversed). 68The include file 69.In netinet/in.h 70defines this address 71as a discriminated union. 72.Pp 73Sockets bound to the Internet protocol family utilize 74the following addressing structure, 75.Bd -literal -offset indent 76struct sockaddr_in { 77 uint8_t sin_len; 78 sa_family_t sin_family; 79 in_port_t sin_port; 80 struct in_addr sin_addr; 81 char sin_zero[8]; 82}; 83.Ed 84.Pp 85Sockets may be created with the local address 86.Dv INADDR_ANY 87to affect 88.Dq wildcard 89matching on incoming messages. 90The address in a 91.Xr connect 2 92or 93.Xr sendto 2 94call may be given as 95.Dv INADDR_ANY 96to mean 97.Dq this host . 98The distinguished address 99.Dv INADDR_BROADCAST 100is allowed as a shorthand for the broadcast address on the primary 101network if the first network configured supports broadcast. 102.Sh PROTOCOLS 103The Internet protocol family is comprised of 104the 105.Tn IP 106network protocol, Internet Control 107Message Protocol 108.Pq Tn ICMP , 109Internet Group Management Protocol 110.Pq Tn IGMP , 111Transmission Control 112Protocol 113.Pq Tn TCP , 114and User Datagram Protocol 115.Pq Tn UDP . 116.Tn TCP 117is used to support the 118.Dv SOCK_STREAM 119abstraction while 120.Tn UDP 121is used to support the 122.Dv SOCK_DGRAM 123abstraction. 124A raw interface to 125.Tn IP 126is available 127by creating an Internet socket of type 128.Dv SOCK_RAW . 129The 130.Tn ICMP 131message protocol is accessible from a raw socket. 132.Pp 133The 32-bit Internet address contains both network and host parts. 134However, direct examination of addresses is discouraged. 135For those 136programs which absolutely need to break addresses into their component 137parts, the following 138.Xr ioctl 2 139commands are provided for a datagram socket in the Internet domain; 140they have the same form as the 141.Dv SIOCIFADDR 142command (see 143.Xr intro 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.Ss MIB Variables 154A number of variables are implemented in the net.inet branch of the 155.Xr sysctl 3 156MIB. 157In addition to the variables supported by the transport protocols 158(for which the respective manual pages may be consulted), 159the following general variables are defined: 160.Bl -tag -width IPCTL_FASTFORWARDING 161.It Dv IPCTL_FORWARDING 162.Pq ip.forwarding 163Boolean: enable/disable forwarding of IP packets. 164Defaults to off. 165.It Dv IPCTL_FASTFORWARDING 166.Pq ip.fastforwarding 167Boolean: enable/disable the use of 168.Tn fast IP forwarding 169code. 170Defaults to off. 171When 172.Tn fast IP forwarding 173is enabled, IP packets are forwarded directly to the appropriate network 174interface with direct processing to completion, which greatly improves 175the throughput. 176All packets for local IP addresses, non-unicast, or with IP options are 177handled by the normal IP input processing path. 178All features of the normal (slow) IP forwarding path are supported 179including firewall (through 180.Xr pfil 9 181hooks) checking, except 182.Xr ipsec 4 183tunnel brokering. 184The 185.Tn IP fastforwarding 186path does not generate ICMP redirect or source quench messages. 187.It Dv IPCTL_SENDREDIRECTS 188.Pq ip.redirect 189Boolean: enable/disable sending of ICMP redirects in response to 190.Tn IP 191packets for which a better, and for the sender directly reachable, route 192and next hop is known. 193Defaults to on. 194.It Dv IPCTL_DEFTTL 195.Pq ip.ttl 196Integer: default time-to-live 197.Pq Dq TTL 198to use for outgoing 199.Tn IP 200packets. 201.It Dv IPCTL_ACCEPTSOURCEROUTE 202.Pq ip.accept_sourceroute 203Boolean: enable/disable accepting of source-routed IP packets (default false). 204.It Dv IPCTL_SOURCEROUTE 205.Pq ip.sourceroute 206Boolean: enable/disable forwarding of source-routed IP packets (default false). 207.It Dv IPCTL_RTEXPIRE 208.Pq ip.rtexpire 209Integer: lifetime in seconds of protocol-cloned 210.Tn IP 211routes after the last reference drops (default one hour). 212This value varies dynamically as described above. 213.It Dv IPCTL_RTMINEXPIRE 214.Pq ip.rtminexpire 215Integer: minimum value of ip.rtexpire (default ten seconds). 216This value has no effect on user modifications, but restricts the dynamic 217adaptation described above. 218.It Dv IPCTL_RTMAXCACHE 219.Pq ip.rtmaxcache 220Integer: trigger level of cached, unreferenced, protocol-cloned routes 221which initiates dynamic adaptation (default 128). 222.It Va ip.process_options 223Integer: control IP options processing. 224By setting this variable to 0, all IP options in the incoming packets 225will be ignored, and the packets will be passed unmodified. 226By setting to 1, IP options in the incoming packets will be processed 227accordingly. 228By setting to 2, an 229.Tn ICMP 230.Dq "prohibited by filter" 231message will be sent back in response to incoming packets with IP options. 232Default is 1. 233This 234.Xr sysctl 8 235variable affects packets destined for a local host as well as packets 236forwarded to some other host. 237.It Va ip.random_id 238Boolean: control IP IDs generation behaviour. 239Setting this 240.Xr sysctl 8 241to non-zero causes the ID field in IP packets to be randomized instead of 242incremented by 1 with each packet generated. 243This closes a minor information leak which allows remote observers to 244determine the rate of packet generation on the machine by watching the 245counter. 246In the same time, on high-speed links, it can decrease the ID reuse 247cycle greatly. 248Default is 0 (sequential IP IDs). 249IPv6 flow IDs and fragment IDs are always random. 250.It Va ip.maxfragpackets 251Integer: maximum number of fragmented packets the host will accept and hold 252in the reassembling queue simultaneously. 2530 means that the host will not accept any fragmented packets. 254\-1 means that the host will accept as many fragmented packets as it receives. 255.It Va ip.maxfragsperpacket 256Integer: maximum number of fragments the host will accept and hold 257in the reassembling queue for a packet. 2580 means that the host will not accept any fragmented packets. 259.El 260.Sh SEE ALSO 261.Xr ioctl 2 , 262.Xr socket 2 , 263.Xr sysctl 3 , 264.Xr icmp 4 , 265.Xr intro 4 , 266.Xr ip 4 , 267.Xr ipfirewall 4 , 268.Xr route 4 , 269.Xr tcp 4 , 270.Xr udp 4 , 271.Xr pfil 9 272.Rs 273.%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" 274.%B PS1 275.%N 7 276.Re 277.Rs 278.%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" 279.%B PS1 280.%N 8 281.Re 282.Sh HISTORY 283The 284.Nm 285protocol interface appeared in 286.Bx 4.2 . 287The 288.Dq protocol cloning 289code appeared in 290.Fx 2.1 . 291.Sh CAVEATS 292The Internet protocol support is subject to change as 293the Internet protocols develop. 294Users should not depend 295on details of the current implementation, but rather 296the services exported. 297