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.\" @(#)ip.4 8.2 (Berkeley) 11/30/93 33.\" $FreeBSD: src/share/man/man4/ip.4,v 1.13.2.9 2002/05/02 02:40:26 silby Exp $ 34.\" $DragonFly: src/share/man/man4/ip.4,v 1.3 2006/02/10 19:01:09 swildner Exp $ 35.\" 36.Dd March 3, 2001 37.Dt IP 4 38.Os 39.Sh NAME 40.Nm ip 41.Nd Internet Protocol 42.Sh SYNOPSIS 43.In sys/types.h 44.In sys/socket.h 45.In netinet/in.h 46.Ft int 47.Fn socket AF_INET SOCK_RAW proto 48.Sh DESCRIPTION 49.Tn IP 50is the transport layer protocol used 51by the Internet protocol family. 52Options may be set at the 53.Tn IP 54level 55when using higher-level protocols that are based on 56.Tn IP 57(such as 58.Tn TCP 59and 60.Tn UDP ) . 61It may also be accessed 62through a 63.Dq raw socket 64when developing new protocols, or 65special-purpose applications. 66.Pp 67There are several 68.Tn IP-level 69.Xr setsockopt 2 70and 71.Xr getsockopt 2 72options. 73.Dv IP_OPTIONS 74may be used to provide 75.Tn IP 76options to be transmitted in the 77.Tn IP 78header of each outgoing packet 79or to examine the header options on incoming packets. 80.Tn IP 81options may be used with any socket type in the Internet family. 82The format of 83.Tn IP 84options to be sent is that specified by the 85.Tn IP 86protocol specification (RFC-791), with one exception: 87the list of addresses for Source Route options must include the first-hop 88gateway at the beginning of the list of gateways. 89The first-hop gateway address will be extracted from the option list 90and the size adjusted accordingly before use. 91To disable previously specified options, 92use a zero-length buffer: 93.Bd -literal 94setsockopt(s, IPPROTO_IP, IP_OPTIONS, NULL, 0); 95.Ed 96.Pp 97.Dv IP_TOS 98and 99.Dv IP_TTL 100may be used to set the type-of-service and time-to-live 101fields in the 102.Tn IP 103header for 104.Dv SOCK_STREAM , SOCK_DGRAM , 105and certain types of 106.Dv SOCK_RAW 107sockets. 108For example, 109.Bd -literal 110int tos = IPTOS_LOWDELAY; /* see <netinet/ip.h> */ 111setsockopt(s, IPPROTO_IP, IP_TOS, &tos, sizeof(tos)); 112 113int ttl = 60; /* max = 255 */ 114setsockopt(s, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl)); 115.Ed 116.Pp 117If the 118.Dv IP_RECVDSTADDR 119option is enabled on a 120.Dv SOCK_DGRAM 121socket, 122the 123.Xr recvmsg 2 124call will return the destination 125.Tn IP 126address for a 127.Tn UDP 128datagram. 129The msg_control field in the msghdr structure points to a buffer 130that contains a cmsghdr structure followed by the 131.Tn IP 132address. 133The cmsghdr fields have the following values: 134.Bd -literal 135cmsg_len = sizeof(struct in_addr) 136cmsg_level = IPPROTO_IP 137cmsg_type = IP_RECVDSTADDR 138.Ed 139.Pp 140.Dv IP_PORTRANGE 141may be used to set the port range used for selecting a local port number 142on a socket with an unspecified (zero) port number. 143It has the following 144possible values: 145.Bl -tag -width IP_PORTRANGE_DEFAULT 146.It Dv IP_PORTRANGE_DEFAULT 147use the default range of values, normally 148.Dv IPPORT_RESERVED 149through 150.Dv IPPORT_USERRESERVED . 151This is adjustable through the sysctl setting: 152.Sy net.inet.ip.portrange.first 153and 154.Sy net.inet.ip.portrange.last . 155.It Dv IP_PORTRANGE_HIGH 156use a high range of values, normally 157.Dv IPPORT_HIFIRSTAUTO 158and 159.Dv IPPORT_HILASTAUTO . 160This is adjustable through the sysctl setting: 161.Sy net.inet.ip.portrange.hifirst 162and 163.Sy net.inet.ip.portrange.hilast . 164.It Dv IP_PORTRANGE_LOW 165use a low range of ports, which are normally restricted to 166privileged processes on 167.Ux 168systems. The range is normally from 169.Dv IPPORT_RESERVED - 1 170down to 171.Li IPPORT_RESERVEDSTART 172in descending order. 173This is adjustable through the sysctl setting: 174.Sy net.inet.ip.portrange.lowfirst 175and 176.Sy net.inet.ip.portrange.lowlast . 177.El 178.Ss "Multicast Options" 179.Tn IP 180multicasting is supported only on 181.Dv AF_INET 182sockets of type 183.Dv SOCK_DGRAM 184and 185.Dv SOCK_RAW , 186and only on networks where the interface 187driver supports multicasting. 188.Pp 189The 190.Dv IP_MULTICAST_TTL 191option changes the time-to-live (TTL) 192for outgoing multicast datagrams 193in order to control the scope of the multicasts: 194.Bd -literal 195u_char ttl; /* range: 0 to 255, default = 1 */ 196setsockopt(s, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl)); 197.Ed 198.Pp 199Datagrams with a TTL of 1 are not forwarded beyond the local network. 200Multicast datagrams with a TTL of 0 will not be transmitted on any network, 201but may be delivered locally if the sending host belongs to the destination 202group and if multicast loopback has not been disabled on the sending socket 203(see below). Multicast datagrams with TTL greater than 1 may be forwarded 204to other networks if a multicast router is attached to the local network. 205.Pp 206For hosts with multiple interfaces, each multicast transmission is 207sent from the primary network interface. 208The 209.Dv IP_MULTICAST_IF 210option overrides the default for 211subsequent transmissions from a given socket: 212.Bd -literal 213struct in_addr addr; 214setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF, &addr, sizeof(addr)); 215.Ed 216.Pp 217where "addr" is the local 218.Tn IP 219address of the desired interface or 220.Dv INADDR_ANY 221to specify the default interface. 222An interface's local IP address and multicast capability can 223be obtained via the 224.Dv SIOCGIFCONF 225and 226.Dv SIOCGIFFLAGS 227ioctls. 228Normal applications should not need to use this option. 229.Pp 230If a multicast datagram is sent to a group to which the sending host itself 231belongs (on the outgoing interface), a copy of the datagram is, by default, 232looped back by the IP layer for local delivery. 233The 234.Dv IP_MULTICAST_LOOP 235option gives the sender explicit control 236over whether or not subsequent datagrams are looped back: 237.Bd -literal 238u_char loop; /* 0 = disable, 1 = enable (default) */ 239setsockopt(s, IPPROTO_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop)); 240.Ed 241.Pp 242This option 243improves performance for applications that may have no more than one 244instance on a single host (such as a router daemon), by eliminating 245the overhead of receiving their own transmissions. It should generally not 246be used by applications for which there may be more than one instance on a 247single host (such as a conferencing program) or for which the sender does 248not belong to the destination group (such as a time querying program). 249.Pp 250A multicast datagram sent with an initial TTL greater than 1 may be delivered 251to the sending host on a different interface from that on which it was sent, 252if the host belongs to the destination group on that other interface. The 253loopback control option has no effect on such delivery. 254.Pp 255A host must become a member of a multicast group before it can receive 256datagrams sent to the group. To join a multicast group, use the 257.Dv IP_ADD_MEMBERSHIP 258option: 259.Bd -literal 260struct ip_mreq mreq; 261setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq)); 262.Ed 263.Pp 264where 265.Fa mreq 266is the following structure: 267.Bd -literal 268struct ip_mreq { 269 struct in_addr imr_multiaddr; /* IP multicast address of group */ 270 struct in_addr imr_interface; /* local IP address of interface */ 271} 272.Ed 273.Pp 274.Dv imr_interface 275should 276be 277.Dv INADDR_ANY 278to choose the default multicast interface, 279or the 280.Tn IP 281address of a particular multicast-capable interface if 282the host is multihomed. 283Membership is associated with a single interface; 284programs running on multihomed hosts may need to 285join the same group on more than one interface. 286Up to 287.Dv IP_MAX_MEMBERSHIPS 288(currently 20) memberships may be added on a 289single socket. 290.Pp 291To drop a membership, use: 292.Bd -literal 293struct ip_mreq mreq; 294setsockopt(s, IPPROTO_IP, IP_DROP_MEMBERSHIP, &mreq, sizeof(mreq)); 295.Ed 296.Pp 297where 298.Fa mreq 299contains the same values as used to add the membership. 300Memberships are dropped when the socket is closed or the process exits. 301.\"----------------------- 302.Ss "Raw IP Sockets" 303Raw 304.Tn IP 305sockets are connectionless, 306and are normally used with the 307.Xr sendto 2 308and 309.Xr recvfrom 2 310calls, though the 311.Xr connect 2 312call may also be used to fix the destination for future 313packets (in which case the 314.Xr read 2 315or 316.Xr recv 2 317and 318.Xr write 2 319or 320.Xr send 2 321system calls may be used). 322.Pp 323If 324.Fa proto 325is 0, the default protocol 326.Dv IPPROTO_RAW 327is used for outgoing 328packets, and only incoming packets destined for that protocol 329are received. 330If 331.Fa proto 332is non-zero, that protocol number will be used on outgoing packets 333and to filter incoming packets. 334.Pp 335Outgoing packets automatically have an 336.Tn IP 337header prepended to 338them (based on the destination address and the protocol 339number the socket is created with), 340unless the 341.Dv IP_HDRINCL 342option has been set. 343Incoming packets are received with 344.Tn IP 345header and options intact. 346.Pp 347.Dv IP_HDRINCL 348indicates the complete IP header is included with the data 349and may be used only with the 350.Dv SOCK_RAW 351type. 352.Bd -literal 353#include <netinet/in_systm.h> 354#include <netinet/ip.h> 355 356int hincl = 1; /* 1 = on, 0 = off */ 357setsockopt(s, IPPROTO_IP, IP_HDRINCL, &hincl, sizeof(hincl)); 358.Ed 359.Pp 360Unlike previous 361.Bx 362releases, the program must set all 363the fields of the IP header, including the following: 364.Bd -literal 365ip->ip_v = IPVERSION; 366ip->ip_hl = hlen >> 2; 367ip->ip_id = 0; /* 0 means kernel set appropriate value */ 368ip->ip_off = offset; 369.Ed 370.Pp 371If the header source address is set to 372.Dv INADDR_ANY , 373the kernel will choose an appropriate address. 374.Sh ERRORS 375A socket operation may fail with one of the following errors returned: 376.Bl -tag -width Er 377.It Bq Er EISCONN 378when trying to establish a connection on a socket which 379already has one, or when trying to send a datagram with the destination 380address specified and the socket is already connected; 381.It Bq Er ENOTCONN 382when trying to send a datagram, but 383no destination address is specified, and the socket hasn't been 384connected; 385.It Bq Er ENOBUFS 386when the system runs out of memory for 387an internal data structure; 388.It Bq Er EADDRNOTAVAIL 389when an attempt is made to create a 390socket with a network address for which no network interface 391exists. 392.It Bq Er EACCES 393when an attempt is made to create 394a raw IP socket by a non-privileged process. 395.El 396.Pp 397The following errors specific to 398.Tn IP 399may occur when setting or getting 400.Tn IP 401options: 402.Bl -tag -width EADDRNOTAVAILxx 403.It Bq Er EINVAL 404An unknown socket option name was given. 405.It Bq Er EINVAL 406The IP option field was improperly formed; 407an option field was shorter than the minimum value 408or longer than the option buffer provided. 409.El 410.Sh SEE ALSO 411.Xr getsockopt 2 , 412.Xr recv 2 , 413.Xr send 2 , 414.Xr icmp 4 , 415.Xr inet 4 , 416.Xr intro 4 417.Sh HISTORY 418The 419.Nm 420protocol appeared in 421.Bx 4.2 . 422