1.\" $NetBSD: ip.4,v 1.16 2003/09/07 16:22:28 wiz Exp $ 2.\" 3.\" Copyright (c) 1983, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)ip.4 8.2 (Berkeley) 11/30/93 31.\" 32.Dd November 30, 1993 33.Dt IP 4 34.Os 35.Sh NAME 36.Nm ip 37.Nd Internet Protocol 38.Sh SYNOPSIS 39.In sys/socket.h 40.In netinet/in.h 41.Ft int 42.Fn socket AF_INET SOCK_RAW proto 43.Sh DESCRIPTION 44.Tn IP 45is the network layer protocol used by the Internet protocol family. 46Options may be set at the 47.Tn IP 48level when using higher-level protocols that are based on 49.Tn IP 50(such as 51.Tn TCP 52and 53.Tn UDP ) . 54It may also be accessed through a 55.Dq raw socket 56when developing new protocols, or special-purpose applications. 57.Pp 58There are several 59.Tn IP-level 60.Xr setsockopt 2 Ns / Ns Xr getsockopt 2 61options. 62.Dv IP_OPTIONS 63may be used to provide 64.Tn IP 65options to be transmitted in the 66.Tn IP 67header of each outgoing packet 68or to examine the header options on incoming packets. 69.Tn IP 70options may be used with any socket type in the Internet family. 71The format of 72.Tn IP 73options to be sent is that specified by the 74.Tn IP 75protocol specification (RFC 791), with one exception: 76the list of addresses for Source Route options must include the first-hop 77gateway at the beginning of the list of gateways. 78The first-hop gateway address will be extracted from the option list 79and the size adjusted accordingly before use. 80To disable previously specified options, use a zero-length buffer: 81.Bd -literal 82setsockopt(s, IPPROTO_IP, IP_OPTIONS, NULL, 0); 83.Ed 84.Pp 85.Dv IP_TOS 86and 87.Dv IP_TTL 88may be used to set the type-of-service and time-to-live fields in the 89.Tn IP 90header for 91.Dv SOCK_STREAM 92and 93.Dv SOCK_DGRAM 94sockets. 95For example, 96.Bd -literal 97int tos = IPTOS_LOWDELAY; /* see \*[Lt]netinet/in.h\*[Gt] */ 98setsockopt(s, IPPROTO_IP, IP_TOS, \*[Am]tos, sizeof(tos)); 99 100int ttl = 60; /* max = 255 */ 101setsockopt(s, IPPROTO_IP, IP_TTL, \*[Am]ttl, sizeof(ttl)); 102.Ed 103.Pp 104.Dv IP_PORTRANGE 105controls how ephemeral ports are allocated for 106.Dv SOCK_STREAM 107and 108.Dv SOCK_DGRAM 109sockets. For example, 110.Bd -literal 111int range = IP_PORTRANGE_LOW; /* see \*[Lt]netinet/in.h\*[Gt] */ 112setsockopt(s, IPPROTO_IP, IP_PORTRANGE, \*[Am]range, sizeof(range)); 113.Ed 114.Pp 115If the 116.Dv IP_RECVDSTADDR 117option is enabled on a 118.Dv SOCK_DGRAM 119or 120.Dv SOCK_RAW 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 140If the 141.Dv IP_RECVIF 142option is enabled on a 143.Dv SOCK_DGRAM 144or 145.Dv SOCK_RAW 146socket, 147the 148.Xr recvmsg 2 149call will return a struct sockaddr_dl corresponding to 150the interface on which the packet was received. 151the msg_control field in the msghdr structure points to a buffer 152that contains a cmsghdr structure followed by the struct sockaddr_dl. 153The cmsghdr fields have the following values: 154.Bd -literal 155cmsg_len = sizeof(struct sockaddr_dl) 156cmsg_level = IPPROTO_IP 157cmsg_type = IP_RECVIF 158.Ed 159.Ss MULTICAST OPTIONS 160.Tn IP 161multicasting is supported only on 162.Dv AF_INET 163sockets of type 164.Dv SOCK_DGRAM 165and 166.Dv SOCK_RAW , 167and only on networks where the interface driver supports multicasting. 168.Pp 169The 170.Dv IP_MULTICAST_TTL 171option changes the time-to-live (TTL) for outgoing multicast datagrams 172in order to control the scope of the multicasts: 173.Bd -literal 174u_char ttl; /* range: 0 to 255, default = 1 */ 175setsockopt(s, IPPROTO_IP, IP_MULTICAST_TTL, \*[Am]ttl, sizeof(ttl)); 176.Ed 177.Pp 178Datagrams with a TTL of 1 are not forwarded beyond the local network. 179Multicast datagrams with a TTL of 0 will not be transmitted on any network, 180but may be delivered locally if the sending host belongs to the destination 181group and if multicast loopback has not been disabled on the sending socket 182(see below). 183Multicast datagrams with TTL greater than 1 may be forwarded 184to other networks if a multicast router is attached to the local network. 185.Pp 186For hosts with multiple interfaces, each multicast transmission is 187sent from the primary network interface. 188The 189.Dv IP_MULTICAST_IF 190option overrides the default for 191subsequent transmissions from a given socket: 192.Bd -literal 193struct in_addr addr; 194setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF, \*[Am]addr, sizeof(addr)); 195.Ed 196.Pp 197where "addr" is the local 198.Tn IP 199address of the desired interface or 200.Dv INADDR_ANY 201to specify the default interface. 202An interface's local IP address and multicast capability can 203be obtained via the 204.Dv SIOCGIFCONF 205and 206.Dv SIOCGIFFLAGS 207ioctls. 208Normal applications should not need to use this option. 209.Pp 210If a multicast datagram is sent to a group to which the sending host itself 211belongs (on the outgoing interface), a copy of the datagram is, by default, 212looped back by the IP layer for local delivery. 213The 214.Dv IP_MULTICAST_LOOP 215option gives the sender explicit control 216over whether or not subsequent datagrams are looped back: 217.Bd -literal 218u_char loop; /* 0 = disable, 1 = enable (default) */ 219setsockopt(s, IPPROTO_IP, IP_MULTICAST_LOOP, \*[Am]loop, sizeof(loop)); 220.Ed 221.Pp 222This option 223improves performance for applications that may have no more than one 224instance on a single host (such as a router demon), by eliminating 225the overhead of receiving their own transmissions. 226It should generally not be used by applications for which there 227may be more than one instance on a single host (such as a conferencing 228program) or for which the sender does not belong to the destination 229group (such as a time querying program). 230.Pp 231A multicast datagram sent with an initial TTL greater than 1 may be delivered 232to the sending host on a different interface from that on which it was sent, 233if the host belongs to the destination group on that other interface. 234The loopback control option has no effect on such delivery. 235.Pp 236A host must become a member of a multicast group before it can receive 237datagrams sent to the group. 238To join a multicast group, use the 239.Dv IP_ADD_MEMBERSHIP 240option: 241.Bd -literal 242struct ip_mreq mreq; 243setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP, \*[Am]mreq, sizeof(mreq)); 244.Ed 245.Pp 246where 247.Fa mreq 248is the following structure: 249.Bd -literal 250struct ip_mreq { 251 struct in_addr imr_multiaddr; /* multicast group to join */ 252 struct in_addr imr_interface; /* interface to join on */ 253} 254.Ed 255.Pp 256.Dv imr_interface 257should be 258.Dv INADDR_ANY 259to choose the default multicast interface, or the 260.Tn IP 261address of a particular multicast-capable interface if 262the host is multihomed. 263Membership is associated with a single interface; 264programs running on multihomed hosts may need to 265join the same group on more than one interface. 266Up to 267.Dv IP_MAX_MEMBERSHIPS 268(currently 20) memberships may be added on a single socket. 269.Pp 270To drop a membership, use: 271.Bd -literal 272struct ip_mreq mreq; 273setsockopt(s, IPPROTO_IP, IP_DROP_MEMBERSHIP, \*[Am]mreq, sizeof(mreq)); 274.Ed 275.Pp 276where 277.Fa mreq 278contains the same values as used to add the membership. 279Memberships are dropped when the socket is closed or the process exits. 280.\"----------------------- 281.Ss RAW IP SOCKETS 282Raw 283.Tn IP 284sockets are connectionless, and are normally used with the 285.Xr sendto 2 286and 287.Xr recvfrom 2 288calls, though the 289.Xr connect 2 290call may also be used to fix the destination for future 291packets (in which case the 292.Xr read 2 293or 294.Xr recv 2 295and 296.Xr write 2 297or 298.Xr send 2 299system calls may be used). 300.Pp 301If 302.Fa proto 303is 0, the default protocol 304.Dv IPPROTO_RAW 305is used for outgoing packets, and only incoming packets destined 306for that protocol are received. 307If 308.Fa proto 309is non-zero, that protocol number will be used on outgoing packets 310and to filter incoming packets. 311.Pp 312Outgoing packets automatically have an 313.Tn IP 314header prepended to them (based on the destination address and the 315protocol number the socket is created with), unless the 316.Dv IP_HDRINCL 317option has been set. 318Incoming packets are received with 319.Tn IP 320header and options intact. 321.Pp 322.Dv IP_HDRINCL 323indicates the complete IP header is included with the data and may 324be used only with the 325.Dv SOCK_RAW 326type. 327.Bd -literal 328#include \*[Lt]netinet/ip.h\*[Gt] 329 330int hincl = 1; /* 1 = on, 0 = off */ 331setsockopt(s, IPPROTO_IP, IP_HDRINCL, \*[Am]hincl, sizeof(hincl)); 332.Ed 333.Pp 334Unlike previous 335.Bx 336releases, the program must set all 337the fields of the IP header, including the following: 338.Bd -literal 339ip-\*[Gt]ip_v = IPVERSION; 340ip-\*[Gt]ip_hl = hlen \*[Gt]\*[Gt] 2; 341ip-\*[Gt]ip_id = 0; /* 0 means kernel set appropriate value */ 342ip-\*[Gt]ip_off = offset; 343.Ed 344.Pp 345If the header source address is set to 346.Dv INADDR_ANY , 347the kernel will choose an appropriate address. 348.Sh DIAGNOSTICS 349A socket operation may fail with one of the following errors returned: 350.Bl -tag -width [EADDRNOTAVAIL] 351.It Bq Er EISCONN 352when trying to establish a connection on a socket which already 353has one, or when trying to send a datagram with the destination 354address specified and the socket is already connected; 355.It Bq Er ENOTCONN 356when trying to send a datagram, but no destination address is 357specified, and the socket hasn't been connected; 358.It Bq Er ENOBUFS 359when the system runs out of memory for an internal data structure; 360.It Bq Er EADDRNOTAVAIL 361when an attempt is made to create a socket with a network address 362for which no network interface exists. 363.It Bq Er EACCES 364when an attempt is made to create a raw IP socket by a non-privileged process. 365.El 366.Pp 367The following errors specific to 368.Tn IP 369may occur when setting or getting 370.Tn IP 371options: 372.Bl -tag -width EADDRNOTAVAILxx 373.It Bq Er EINVAL 374An unknown socket option name was given. 375.It Bq Er EINVAL 376The IP option field was improperly formed; an option field was 377shorter than the minimum value or longer than the option buffer provided. 378.El 379.Sh SEE ALSO 380.Xr getsockopt 2 , 381.Xr recv 2 , 382.Xr send 2 , 383.Xr icmp 4 , 384.Xr inet 4 , 385.Xr intro 4 386.Rs 387.%R RFC 388.%N 791 389.%D September 1981 390.%T "Internet Protocol" 391.Re 392.Rs 393.%R RFC 394.%N 1112 395.%D August 1989 396.%T "Host Extensions for IP Multicasting" 397.Re 398.Rs 399.%R RFC 400.%N 1122 401.%D October 1989 402.%T "Requirements for Internet Hosts -- Communication Layers" 403.Re 404.Sh HISTORY 405The 406.Nm 407protocol appeared in 408.Bx 4.2 . 409