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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 $
34 .\" $DragonFly: src/share/man/man4/ip.4,v 1.2 2003/06/17 04:36:59 dillon Exp $
47 .Fn socket AF_INET SOCK_RAW proto
50 is the transport layer protocol used
51 by the Internet protocol family.
52 Options may be set at the
55 when using higher-level protocols that are based on
61 It may also be accessed
64 when developing new protocols, or
65 special-purpose applications.
74 may be used to provide
76 options to be transmitted in the
78 header of each outgoing packet
79 or to examine the header options on incoming packets.
81 options may be used with any socket type in the Internet family.
84 options to be sent is that specified by the
86 protocol specification (RFC-791), with one exception:
87 the list of addresses for Source Route options must include the first-hop
88 gateway at the beginning of the list of gateways.
89 The first-hop gateway address will be extracted from the option list
90 and the size adjusted accordingly before use.
91 To disable previously specified options,
92 use a zero-length buffer:
94 setsockopt(s, IPPROTO_IP, IP_OPTIONS, NULL, 0);
100 may be used to set the type-of-service and time-to-live
104 .Dv SOCK_STREAM , SOCK_DGRAM ,
110 int tos = IPTOS_LOWDELAY; /* see <netinet/ip.h> */
111 setsockopt(s, IPPROTO_IP, IP_TOS, &tos, sizeof(tos));
113 int ttl = 60; /* max = 255 */
114 setsockopt(s, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
119 option is enabled on a
124 call will return the destination
129 The msg_control field in the msghdr structure points to a buffer
130 that contains a cmsghdr structure followed by the
133 The cmsghdr fields have the following values:
135 cmsg_len = sizeof(struct in_addr)
136 cmsg_level = IPPROTO_IP
137 cmsg_type = IP_RECVDSTADDR
141 may be used to set the port range used for selecting a local port number
142 on a socket with an unspecified (zero) port number.
145 .Bl -tag -width IP_PORTRANGE_DEFAULT
146 .It Dv IP_PORTRANGE_DEFAULT
147 use the default range of values, normally
150 .Dv IPPORT_USERRESERVED .
151 This is adjustable through the sysctl setting:
152 .Sy net.inet.ip.portrange.first
154 .Sy net.inet.ip.portrange.last .
155 .It Dv IP_PORTRANGE_HIGH
156 use a high range of values, normally
157 .Dv IPPORT_HIFIRSTAUTO
159 .Dv IPPORT_HILASTAUTO .
160 This is adjustable through the sysctl setting:
161 .Sy net.inet.ip.portrange.hifirst
163 .Sy net.inet.ip.portrange.hilast .
164 .It Dv IP_PORTRANGE_LOW
165 use a low range of ports, which are normally restricted to
166 privileged processes on
168 systems. The range is normally from
169 .Dv IPPORT_RESERVED - 1
171 .Li IPPORT_RESERVEDSTART
173 This is adjustable through the sysctl setting:
174 .Sy net.inet.ip.portrange.lowfirst
176 .Sy net.inet.ip.portrange.lowlast .
178 .Ss "Multicast Options"
181 multicasting is supported only on
187 and only on networks where the interface
188 driver supports multicasting.
192 option changes the time-to-live (TTL)
193 for outgoing multicast datagrams
194 in order to control the scope of the multicasts:
196 u_char ttl; /* range: 0 to 255, default = 1 */
197 setsockopt(s, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
200 Datagrams with a TTL of 1 are not forwarded beyond the local network.
201 Multicast datagrams with a TTL of 0 will not be transmitted on any network,
202 but may be delivered locally if the sending host belongs to the destination
203 group 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
205 to other networks if a multicast router is attached to the local network.
207 For hosts with multiple interfaces, each multicast transmission is
208 sent from the primary network interface.
211 option overrides the default for
212 subsequent transmissions from a given socket:
215 setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF, &addr, sizeof(addr));
218 where "addr" is the local
220 address of the desired interface or
222 to specify the default interface.
223 An interface's local IP address and multicast capability can
229 Normal applications should not need to use this option.
231 If a multicast datagram is sent to a group to which the sending host itself
232 belongs (on the outgoing interface), a copy of the datagram is, by default,
233 looped back by the IP layer for local delivery.
235 .Dv IP_MULTICAST_LOOP
236 option gives the sender explicit control
237 over whether or not subsequent datagrams are looped back:
239 u_char loop; /* 0 = disable, 1 = enable (default) */
240 setsockopt(s, IPPROTO_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop));
244 improves performance for applications that may have no more than one
245 instance on a single host (such as a router daemon), by eliminating
246 the overhead of receiving their own transmissions. It should generally not
247 be used by applications for which there may be more than one instance on a
248 single host (such as a conferencing program) or for which the sender does
249 not belong to the destination group (such as a time querying program).
251 A multicast datagram sent with an initial TTL greater than 1 may be delivered
252 to the sending host on a different interface from that on which it was sent,
253 if the host belongs to the destination group on that other interface. The
254 loopback control option has no effect on such delivery.
256 A host must become a member of a multicast group before it can receive
257 datagrams sent to the group. To join a multicast group, use the
258 .Dv IP_ADD_MEMBERSHIP
262 setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));
267 is the following structure:
270 struct in_addr imr_multiaddr; /* IP multicast address of group */
271 struct in_addr imr_interface; /* local IP address of interface */
279 to choose the default multicast interface,
282 address of a particular multicast-capable interface if
283 the host is multihomed.
284 Membership is associated with a single interface;
285 programs running on multihomed hosts may need to
286 join the same group on more than one interface.
288 .Dv IP_MAX_MEMBERSHIPS
289 (currently 20) memberships may be added on a
292 To drop a membership, use:
295 setsockopt(s, IPPROTO_IP, IP_DROP_MEMBERSHIP, &mreq, sizeof(mreq));
300 contains the same values as used to add the membership.
301 Memberships are dropped when the socket is closed or the process exits.
302 .\"-----------------------
307 sockets are connectionless,
308 and are normally used with the
314 call may also be used to fix the destination for future
315 packets (in which case the
323 system calls may be used).
327 is 0, the default protocol
330 packets, and only incoming packets destined for that protocol
334 is non-zero, that protocol number will be used on outgoing packets
335 and to filter incoming packets.
337 Outgoing packets automatically have an
340 them (based on the destination address and the protocol
341 number the socket is created with),
345 Incoming packets are received with
347 header and options intact.
350 indicates the complete IP header is included with the data
351 and may be used only with the
355 #include <netinet/in_systm.h>
356 #include <netinet/ip.h>
358 int hincl = 1; /* 1 = on, 0 = off */
359 setsockopt(s, IPPROTO_IP, IP_HDRINCL, &hincl, sizeof(hincl));
364 releases, the program must set all
365 the fields of the IP header, including the following:
367 ip->ip_v = IPVERSION;
368 ip->ip_hl = hlen >> 2;
369 ip->ip_id = 0; /* 0 means kernel set appropriate value */
373 If the header source address is set to
375 the kernel will choose an appropriate address.
377 A socket operation may fail with one of the following errors returned:
380 when trying to establish a connection on a socket which
381 already has one, or when trying to send a datagram with the destination
382 address specified and the socket is already connected;
384 when trying to send a datagram, but
385 no destination address is specified, and the socket hasn't been
388 when the system runs out of memory for
389 an internal data structure;
390 .It Bq Er EADDRNOTAVAIL
391 when an attempt is made to create a
392 socket with a network address for which no network interface
395 when an attempt is made to create
396 a raw IP socket by a non-privileged process.
399 The following errors specific to
401 may occur when setting or getting
404 .Bl -tag -width EADDRNOTAVAILxx
406 An unknown socket option name was given.
408 The IP option field was improperly formed;
409 an option field was shorter than the minimum value
410 or longer than the option buffer provided.