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 1.2 2003/06/17 04:36:59 dillon 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.Pp 180.Tn IP 181multicasting is supported only on 182.Dv AF_INET 183sockets of type 184.Dv SOCK_DGRAM 185and 186.Dv SOCK_RAW , 187and only on networks where the interface 188driver supports multicasting. 189.Pp 190The 191.Dv IP_MULTICAST_TTL 192option changes the time-to-live (TTL) 193for outgoing multicast datagrams 194in order to control the scope of the multicasts: 195.Bd -literal 196u_char ttl; /* range: 0 to 255, default = 1 */ 197setsockopt(s, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl)); 198.Ed 199.Pp 200Datagrams with a TTL of 1 are not forwarded beyond the local network. 201Multicast datagrams with a TTL of 0 will not be transmitted on any network, 202but may be delivered locally if the sending host belongs to the destination 203group and if multicast loopback has not been disabled on the sending socket 204(see below). Multicast datagrams with TTL greater than 1 may be forwarded 205to other networks if a multicast router is attached to the local network. 206.Pp 207For hosts with multiple interfaces, each multicast transmission is 208sent from the primary network interface. 209The 210.Dv IP_MULTICAST_IF 211option overrides the default for 212subsequent transmissions from a given socket: 213.Bd -literal 214struct in_addr addr; 215setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF, &addr, sizeof(addr)); 216.Ed 217.Pp 218where "addr" is the local 219.Tn IP 220address of the desired interface or 221.Dv INADDR_ANY 222to specify the default interface. 223An interface's local IP address and multicast capability can 224be obtained via the 225.Dv SIOCGIFCONF 226and 227.Dv SIOCGIFFLAGS 228ioctls. 229Normal applications should not need to use this option. 230.Pp 231If a multicast datagram is sent to a group to which the sending host itself 232belongs (on the outgoing interface), a copy of the datagram is, by default, 233looped back by the IP layer for local delivery. 234The 235.Dv IP_MULTICAST_LOOP 236option gives the sender explicit control 237over whether or not subsequent datagrams are looped back: 238.Bd -literal 239u_char loop; /* 0 = disable, 1 = enable (default) */ 240setsockopt(s, IPPROTO_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop)); 241.Ed 242.Pp 243This option 244improves performance for applications that may have no more than one 245instance on a single host (such as a router daemon), by eliminating 246the overhead of receiving their own transmissions. It should generally not 247be used by applications for which there may be more than one instance on a 248single host (such as a conferencing program) or for which the sender does 249not belong to the destination group (such as a time querying program). 250.Pp 251A multicast datagram sent with an initial TTL greater than 1 may be delivered 252to the sending host on a different interface from that on which it was sent, 253if the host belongs to the destination group on that other interface. The 254loopback control option has no effect on such delivery. 255.Pp 256A host must become a member of a multicast group before it can receive 257datagrams sent to the group. To join a multicast group, use the 258.Dv IP_ADD_MEMBERSHIP 259option: 260.Bd -literal 261struct ip_mreq mreq; 262setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq)); 263.Ed 264.Pp 265where 266.Fa mreq 267is the following structure: 268.Bd -literal 269struct ip_mreq { 270 struct in_addr imr_multiaddr; /* IP multicast address of group */ 271 struct in_addr imr_interface; /* local IP address of interface */ 272} 273.Ed 274.Pp 275.Dv imr_interface 276should 277be 278.Dv INADDR_ANY 279to choose the default multicast interface, 280or the 281.Tn IP 282address of a particular multicast-capable interface if 283the host is multihomed. 284Membership is associated with a single interface; 285programs running on multihomed hosts may need to 286join the same group on more than one interface. 287Up to 288.Dv IP_MAX_MEMBERSHIPS 289(currently 20) memberships may be added on a 290single socket. 291.Pp 292To drop a membership, use: 293.Bd -literal 294struct ip_mreq mreq; 295setsockopt(s, IPPROTO_IP, IP_DROP_MEMBERSHIP, &mreq, sizeof(mreq)); 296.Ed 297.Pp 298where 299.Fa mreq 300contains the same values as used to add the membership. 301Memberships are dropped when the socket is closed or the process exits. 302.\"----------------------- 303.Ss "Raw IP Sockets" 304.Pp 305Raw 306.Tn IP 307sockets are connectionless, 308and are normally used with the 309.Xr sendto 2 310and 311.Xr recvfrom 2 312calls, though the 313.Xr connect 2 314call may also be used to fix the destination for future 315packets (in which case the 316.Xr read 2 317or 318.Xr recv 2 319and 320.Xr write 2 321or 322.Xr send 2 323system calls may be used). 324.Pp 325If 326.Fa proto 327is 0, the default protocol 328.Dv IPPROTO_RAW 329is used for outgoing 330packets, and only incoming packets destined for that protocol 331are received. 332If 333.Fa proto 334is non-zero, that protocol number will be used on outgoing packets 335and to filter incoming packets. 336.Pp 337Outgoing packets automatically have an 338.Tn IP 339header prepended to 340them (based on the destination address and the protocol 341number the socket is created with), 342unless the 343.Dv IP_HDRINCL 344option has been set. 345Incoming packets are received with 346.Tn IP 347header and options intact. 348.Pp 349.Dv IP_HDRINCL 350indicates the complete IP header is included with the data 351and may be used only with the 352.Dv SOCK_RAW 353type. 354.Bd -literal 355#include <netinet/in_systm.h> 356#include <netinet/ip.h> 357 358int hincl = 1; /* 1 = on, 0 = off */ 359setsockopt(s, IPPROTO_IP, IP_HDRINCL, &hincl, sizeof(hincl)); 360.Ed 361.Pp 362Unlike previous 363.Bx 364releases, the program must set all 365the fields of the IP header, including the following: 366.Bd -literal 367ip->ip_v = IPVERSION; 368ip->ip_hl = hlen >> 2; 369ip->ip_id = 0; /* 0 means kernel set appropriate value */ 370ip->ip_off = offset; 371.Ed 372.Pp 373If the header source address is set to 374.Dv INADDR_ANY , 375the kernel will choose an appropriate address. 376.Sh ERRORS 377A socket operation may fail with one of the following errors returned: 378.Bl -tag -width Er 379.It Bq Er EISCONN 380when trying to establish a connection on a socket which 381already has one, or when trying to send a datagram with the destination 382address specified and the socket is already connected; 383.It Bq Er ENOTCONN 384when trying to send a datagram, but 385no destination address is specified, and the socket hasn't been 386connected; 387.It Bq Er ENOBUFS 388when the system runs out of memory for 389an internal data structure; 390.It Bq Er EADDRNOTAVAIL 391when an attempt is made to create a 392socket with a network address for which no network interface 393exists. 394.It Bq Er EACCES 395when an attempt is made to create 396a raw IP socket by a non-privileged process. 397.El 398.Pp 399The following errors specific to 400.Tn IP 401may occur when setting or getting 402.Tn IP 403options: 404.Bl -tag -width EADDRNOTAVAILxx 405.It Bq Er EINVAL 406An unknown socket option name was given. 407.It Bq Er EINVAL 408The IP option field was improperly formed; 409an option field was shorter than the minimum value 410or longer than the option buffer provided. 411.El 412.Sh SEE ALSO 413.Xr getsockopt 2 , 414.Xr recv 2 , 415.Xr send 2 , 416.Xr icmp 4 , 417.Xr inet 4 , 418.Xr intro 4 419.Sh HISTORY 420The 421.Nm 422protocol appeared in 423.Bx 4.2 . 424