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32 .\" @(#)ip.4 8.2 (Berkeley) 11/30/93
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
132 structure points to a buffer
135 structure followed by the
140 fields have the following values:
142 cmsg_len = sizeof(struct in_addr)
143 cmsg_level = IPPROTO_IP
144 cmsg_type = IP_RECVDSTADDR
147 The source address to be used for outgoing
149 datagrams on a socket that is not bound to a specific
151 address can be specified as ancillary data with a type code of
153 The msg_control field in the msghdr structure should point to a buffer
156 structure followed by the
159 The cmsghdr fields should have the following values:
161 cmsg_len = sizeof(struct in_addr)
162 cmsg_level = IPPROTO_IP
163 cmsg_type = IP_SENDSRCADDR
168 is defined to have the same value as
174 can be used directly as a control message for
179 option is enabled on a
183 socket, the destination address of outgoing
184 broadcast datagrams on that socket will be forced
185 to the undirected broadcast address,
186 .Dv INADDR_BROADCAST ,
188 This is in contrast to the default behavior of the
189 system, which is to transmit undirected broadcasts
190 via the first network interface with the
191 .Dv IFF_BROADCAST flag set.
193 This option allows applications to choose which
194 interface is used to transmit an undirected broadcast
196 For example, the following code would force an
197 undirected broadcast to be transmitted via the interface
198 configured with the broadcast address 192.168.2.255:
201 struct sockaddr_in sin;
202 u_char onesbcast = 1; /* 0 = disable (default), 1 = enable */
204 setsockopt(s, IPPROTO_IP, IP_ONESBCAST, &onesbcast, sizeof(onesbcast));
205 sin.sin_addr.s_addr = inet_addr("192.168.2.255");
206 sin.sin_port = htons(1234);
207 sendto(s, msg, sizeof(msg), 0, &sin, sizeof(sin));
210 It is the application's responsibility to set the
212 to an appropriate value in order to prevent broadcast storms.
213 The application must have sufficient credentials to set the
215 socket level option, otherwise the
216 .Dv IP_ONESBCAST option has no effect.
220 option is enabled on a
227 (time to live) field for a
230 The msg_control field in the msghdr structure points to a buffer
231 that contains a cmsghdr structure followed by the
233 The cmsghdr fields have the following values:
235 cmsg_len = sizeof(u_char)
236 cmsg_level = IPPROTO_IP
237 cmsg_type = IP_RECVTTL
242 option is enabled on a
247 .Vt "struct sockaddr_dl"
248 corresponding to the interface on which the
254 structure points to a buffer that contains a
256 structure followed by the
257 .Vt "struct sockaddr_dl" .
260 fields have the following values:
262 cmsg_len = sizeof(struct sockaddr_dl)
263 cmsg_level = IPPROTO_IP
264 cmsg_type = IP_RECVIF
268 may be used to set the port range used for selecting a local port number
269 on a socket with an unspecified (zero) port number.
272 .Bl -tag -width IP_PORTRANGE_DEFAULT
273 .It Dv IP_PORTRANGE_DEFAULT
274 use the default range of values, normally
275 .Dv IPPORT_HIFIRSTAUTO
277 .Dv IPPORT_HILASTAUTO .
278 This is adjustable through the sysctl setting:
279 .Va net.inet.ip.portrange.first
281 .Va net.inet.ip.portrange.last .
282 .It Dv IP_PORTRANGE_HIGH
283 use a high range of values, normally
284 .Dv IPPORT_HIFIRSTAUTO
286 .Dv IPPORT_HILASTAUTO .
287 This is adjustable through the sysctl setting:
288 .Va net.inet.ip.portrange.hifirst
290 .Va net.inet.ip.portrange.hilast .
291 .It Dv IP_PORTRANGE_LOW
292 use a low range of ports, which are normally restricted to
293 privileged processes on
296 The range is normally from
299 .Li IPPORT_RESERVEDSTART
301 This is adjustable through the sysctl setting:
302 .Va net.inet.ip.portrange.lowfirst
304 .Va net.inet.ip.portrange.lowlast .
307 The range of privileged ports which only may be opened by
308 root-owned processes may be modified by the
309 .Va net.inet.ip.portrange.reservedlow
311 .Va net.inet.ip.portrange.reservedhigh
313 The values default to the traditional range,
317 (0 through 1023), respectively.
318 Note that these settings do not affect and are not accounted for in the
319 use or calculation of the other
320 .Va net.inet.ip.portrange
322 Changing these values departs from
324 tradition and has security
325 consequences that the administrator should carefully evaluate before
326 modifying these settings.
328 Ports are allocated at random within the specified port range in order
329 to increase the difficulty of random spoofing attacks.
330 In scenarios such as benchmarking, this behavior may be undesirable.
332 .Va net.inet.ip.portrange.randomized
333 can be used to toggle randomization off.
335 .Va net.inet.ip.portrange.randomcps
336 ports have been allocated in the last second, then return to sequential
338 Return to random allocation only once the current port allocation rate
340 .Va net.inet.ip.portrange.randomcps
342 .Va net.inet.ip.portrange.randomtime
344 The default values for
345 .Va net.inet.ip.portrange.randomcps
347 .Va net.inet.ip.portrange.randomtime
348 are 10 port allocations per second and 45 seconds correspondingly.
349 .Ss "Multicast Options"
352 multicasting is supported only on
358 and only on networks where the interface
359 driver supports multicasting.
363 option changes the time-to-live (TTL)
364 for outgoing multicast datagrams
365 in order to control the scope of the multicasts:
367 u_char ttl; /* range: 0 to 255, default = 1 */
368 setsockopt(s, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
371 Datagrams with a TTL of 1 are not forwarded beyond the local network.
372 Multicast datagrams with a TTL of 0 will not be transmitted on any network,
373 but may be delivered locally if the sending host belongs to the destination
374 group and if multicast loopback has not been disabled on the sending socket
376 Multicast datagrams with TTL greater than 1 may be forwarded
377 to other networks if a multicast router is attached to the local network.
379 For hosts with multiple interfaces, each multicast transmission is
380 sent from the primary network interface.
383 option overrides the default for
384 subsequent transmissions from a given socket:
387 setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF, &addr, sizeof(addr));
390 where "addr" is the local
392 address of the desired interface or
394 to specify the default interface.
395 An interface's local IP address and multicast capability can
401 Normal applications should not need to use this option.
403 If a multicast datagram is sent to a group to which the sending host itself
404 belongs (on the outgoing interface), a copy of the datagram is, by default,
405 looped back by the IP layer for local delivery.
407 .Dv IP_MULTICAST_LOOP
408 option gives the sender explicit control
409 over whether or not subsequent datagrams are looped back:
411 u_char loop; /* 0 = disable, 1 = enable (default) */
412 setsockopt(s, IPPROTO_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop));
416 improves performance for applications that may have no more than one
417 instance on a single host (such as a router daemon), by eliminating
418 the overhead of receiving their own transmissions.
419 It should generally not
420 be used by applications for which there may be more than one instance on a
421 single host (such as a conferencing program) or for which the sender does
422 not belong to the destination group (such as a time querying program).
424 A multicast datagram sent with an initial TTL greater than 1 may be delivered
425 to the sending host on a different interface from that on which it was sent,
426 if the host belongs to the destination group on that other interface.
427 The loopback control option has no effect on such delivery.
429 A host must become a member of a multicast group before it can receive
430 datagrams sent to the group.
431 To join a multicast group, use the
432 .Dv IP_ADD_MEMBERSHIP
436 setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));
441 is the following structure:
444 struct in_addr imr_multiaddr; /* IP multicast address of group */
445 struct in_addr imr_interface; /* local IP address of interface */
452 to choose the default multicast interface,
455 address of a particular multicast-capable interface if
456 the host is multihomed.
461 member is within the network range
463 it is treated as an interface index in the system interface MIB,
464 as per the RIP Version 2 MIB Extension (RFC-1724).
466 Membership is associated with a single interface;
467 programs running on multihomed hosts may need to
468 join the same group on more than one interface.
470 .Dv IP_MAX_MEMBERSHIPS
471 (currently 20) memberships may be added on a
474 To drop a membership, use:
477 setsockopt(s, IPPROTO_IP, IP_DROP_MEMBERSHIP, &mreq, sizeof(mreq));
482 contains the same values as used to add the membership.
483 Memberships are dropped when the socket is closed or the process exits.
484 .\"-----------------------
489 sockets are connectionless,
490 and are normally used with the
496 call may also be used to fix the destination for future
497 packets (in which case the
505 system calls may be used).
509 is 0, the default protocol
512 packets, and only incoming packets destined for that protocol
516 is non-zero, that protocol number will be used on outgoing packets
517 and to filter incoming packets.
519 Outgoing packets automatically have an
522 them (based on the destination address and the protocol
523 number the socket is created with),
527 Incoming packets are received with
529 header and options intact.
532 indicates the complete IP header is included with the data
533 and may be used only with the
537 #include <netinet/in_systm.h>
538 #include <netinet/ip.h>
540 int hincl = 1; /* 1 = on, 0 = off */
541 setsockopt(s, IPPROTO_IP, IP_HDRINCL, &hincl, sizeof(hincl));
546 releases, the program must set all
547 the fields of the IP header, including the following:
549 ip->ip_v = IPVERSION;
550 ip->ip_hl = hlen >> 2;
551 ip->ip_id = 0; /* 0 means kernel set appropriate value */
561 be provided in host byte order .
562 All other fields must be provided in network byte order.
565 for more information on network byte order.
568 field is set to 0 then the kernel will choose an
570 If the header source address is set to
572 the kernel will choose an appropriate address.
574 A socket operation may fail with one of the following errors returned:
577 when trying to establish a connection on a socket which
578 already has one, or when trying to send a datagram with the destination
579 address specified and the socket is already connected;
581 when trying to send a datagram, but
582 no destination address is specified, and the socket has not been
585 when the system runs out of memory for
586 an internal data structure;
587 .It Bq Er EADDRNOTAVAIL
588 when an attempt is made to create a
589 socket with a network address for which no network interface
592 when an attempt is made to create
593 a raw IP socket by a non-privileged process.
596 The following errors specific to
598 may occur when setting or getting
603 An unknown socket option name was given.
605 The IP option field was improperly formed;
606 an option field was shorter than the minimum value
607 or longer than the option buffer provided.
610 The following errors may occur when attempting to send
621 field was not equal to the length of the datagram written to the socket.