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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 $
46 .Fn socket AF_INET SOCK_RAW proto
49 is the transport layer protocol used
50 by the Internet protocol family.
51 Options may be set at the
54 when using higher-level protocols that are based on
60 It may also be accessed
63 when developing new protocols, or
64 special-purpose applications.
73 may be used to provide
75 options to be transmitted in the
77 header of each outgoing packet
78 or to examine the header options on incoming packets.
80 options may be used with any socket type in the Internet family.
83 options to be sent is that specified by the
85 protocol specification (RFC-791), with one exception:
86 the list of addresses for Source Route options must include the first-hop
87 gateway at the beginning of the list of gateways.
88 The first-hop gateway address will be extracted from the option list
89 and the size adjusted accordingly before use.
90 To disable previously specified options,
91 use a zero-length buffer:
93 setsockopt(s, IPPROTO_IP, IP_OPTIONS, NULL, 0);
99 may be used to set the type-of-service and time-to-live
103 .Dv SOCK_STREAM , SOCK_DGRAM ,
109 int tos = IPTOS_LOWDELAY; /* see <netinet/ip.h> */
110 setsockopt(s, IPPROTO_IP, IP_TOS, &tos, sizeof(tos));
112 int ttl = 60; /* max = 255 */
113 setsockopt(s, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
118 option is enabled on a
123 call will return the destination
128 The msg_control field in the msghdr structure points to a buffer
129 that contains a cmsghdr structure followed by the
132 The cmsghdr fields have the following values:
134 cmsg_len = sizeof(struct in_addr)
135 cmsg_level = IPPROTO_IP
136 cmsg_type = IP_RECVDSTADDR
140 may be used to set the port range used for selecting a local port number
141 on a socket with an unspecified (zero) port number.
144 .Bl -tag -width IP_PORTRANGE_DEFAULT
145 .It Dv IP_PORTRANGE_DEFAULT
146 use the default range of values, normally
149 .Dv IPPORT_USERRESERVED .
150 This is adjustable through the sysctl setting:
151 .Sy net.inet.ip.portrange.first
153 .Sy net.inet.ip.portrange.last .
154 .It Dv IP_PORTRANGE_HIGH
155 use a high range of values, normally
156 .Dv IPPORT_HIFIRSTAUTO
158 .Dv IPPORT_HILASTAUTO .
159 This is adjustable through the sysctl setting:
160 .Sy net.inet.ip.portrange.hifirst
162 .Sy net.inet.ip.portrange.hilast .
163 .It Dv IP_PORTRANGE_LOW
164 use a low range of ports, which are normally restricted to
165 privileged processes on
167 systems. The range is normally from
168 .Dv IPPORT_RESERVED - 1
170 .Li IPPORT_RESERVEDSTART
172 This is adjustable through the sysctl setting:
173 .Sy net.inet.ip.portrange.lowfirst
175 .Sy net.inet.ip.portrange.lowlast .
177 .Ss "Multicast Options"
180 multicasting is supported only on
186 and only on networks where the interface
187 driver supports multicasting.
191 option changes the time-to-live (TTL)
192 for outgoing multicast datagrams
193 in order to control the scope of the multicasts:
195 u_char ttl; /* range: 0 to 255, default = 1 */
196 setsockopt(s, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
199 Datagrams with a TTL of 1 are not forwarded beyond the local network.
200 Multicast datagrams with a TTL of 0 will not be transmitted on any network,
201 but may be delivered locally if the sending host belongs to the destination
202 group 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
204 to other networks if a multicast router is attached to the local network.
206 For hosts with multiple interfaces, each multicast transmission is
207 sent from the primary network interface.
210 option overrides the default for
211 subsequent transmissions from a given socket:
214 setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF, &addr, sizeof(addr));
217 where "addr" is the local
219 address of the desired interface or
221 to specify the default interface.
222 An interface's local IP address and multicast capability can
228 Normal applications should not need to use this option.
230 If a multicast datagram is sent to a group to which the sending host itself
231 belongs (on the outgoing interface), a copy of the datagram is, by default,
232 looped back by the IP layer for local delivery.
234 .Dv IP_MULTICAST_LOOP
235 option gives the sender explicit control
236 over whether or not subsequent datagrams are looped back:
238 u_char loop; /* 0 = disable, 1 = enable (default) */
239 setsockopt(s, IPPROTO_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop));
243 improves performance for applications that may have no more than one
244 instance on a single host (such as a router daemon), by eliminating
245 the overhead of receiving their own transmissions. It should generally not
246 be used by applications for which there may be more than one instance on a
247 single host (such as a conferencing program) or for which the sender does
248 not belong to the destination group (such as a time querying program).
250 A multicast datagram sent with an initial TTL greater than 1 may be delivered
251 to the sending host on a different interface from that on which it was sent,
252 if the host belongs to the destination group on that other interface. The
253 loopback control option has no effect on such delivery.
255 A host must become a member of a multicast group before it can receive
256 datagrams sent to the group. To join a multicast group, use the
257 .Dv IP_ADD_MEMBERSHIP
261 setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));
266 is the following structure:
269 struct in_addr imr_multiaddr; /* IP multicast address of group */
270 struct in_addr imr_interface; /* local IP address of interface */
278 to choose the default multicast interface,
281 address of a particular multicast-capable interface if
282 the host is multihomed.
283 Membership is associated with a single interface;
284 programs running on multihomed hosts may need to
285 join the same group on more than one interface.
287 .Dv IP_MAX_MEMBERSHIPS
288 (currently 20) memberships may be added on a
291 To drop a membership, use:
294 setsockopt(s, IPPROTO_IP, IP_DROP_MEMBERSHIP, &mreq, sizeof(mreq));
299 contains the same values as used to add the membership.
300 Memberships are dropped when the socket is closed or the process exits.
301 .\"-----------------------
306 sockets are connectionless,
307 and are normally used with the
313 call may also be used to fix the destination for future
314 packets (in which case the
322 system calls may be used).
326 is 0, the default protocol
329 packets, and only incoming packets destined for that protocol
333 is non-zero, that protocol number will be used on outgoing packets
334 and to filter incoming packets.
336 Outgoing packets automatically have an
339 them (based on the destination address and the protocol
340 number the socket is created with),
344 Incoming packets are received with
346 header and options intact.
349 indicates the complete IP header is included with the data
350 and may be used only with the
354 #include <netinet/in_systm.h>
355 #include <netinet/ip.h>
357 int hincl = 1; /* 1 = on, 0 = off */
358 setsockopt(s, IPPROTO_IP, IP_HDRINCL, &hincl, sizeof(hincl));
363 releases, the program must set all
364 the fields of the IP header, including the following:
366 ip->ip_v = IPVERSION;
367 ip->ip_hl = hlen >> 2;
368 ip->ip_id = 0; /* 0 means kernel set appropriate value */
372 If the header source address is set to
374 the kernel will choose an appropriate address.
376 A socket operation may fail with one of the following errors returned:
379 when trying to establish a connection on a socket which
380 already has one, or when trying to send a datagram with the destination
381 address specified and the socket is already connected;
383 when trying to send a datagram, but
384 no destination address is specified, and the socket hasn't been
387 when the system runs out of memory for
388 an internal data structure;
389 .It Bq Er EADDRNOTAVAIL
390 when an attempt is made to create a
391 socket with a network address for which no network interface
394 when an attempt is made to create
395 a raw IP socket by a non-privileged process.
398 The following errors specific to
400 may occur when setting or getting
403 .Bl -tag -width EADDRNOTAVAILxx
405 An unknown socket option name was given.
407 The IP option field was improperly formed;
408 an option field was shorter than the minimum value
409 or longer than the option buffer provided.