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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));
117 may be used to set the minimum acceptable TTL a packet must have when
118 received on a socket.
119 All packets with a lower TTL are silently dropped.
120 This option is only really useful when set to 255, preventing packets
121 from outside the directly connected networks reaching local listeners
125 may be used to set the Don't Fragment flag on IP packets.
126 Currently this option is respected only on
135 sockets, the Don't Fragment flag is controlled by the Path
136 MTU Discovery option.
137 Sending a packet larger than the MTU size of the egress interface,
138 determined by the destination address, returns an
144 option is enabled on a
149 call will return the destination
158 structure points to a buffer
161 structure followed by the
166 fields have the following values:
168 cmsg_len = CMSG_LEN(sizeof(struct in_addr))
169 cmsg_level = IPPROTO_IP
170 cmsg_type = IP_RECVDSTADDR
173 The source address to be used for outgoing
175 datagrams on a socket that is not bound to a specific
177 address can be specified as ancillary data with a type code of
179 The msg_control field in the msghdr structure should point to a buffer
182 structure followed by the
185 The cmsghdr fields should have the following values:
187 cmsg_len = CMSG_LEN(sizeof(struct in_addr))
188 cmsg_level = IPPROTO_IP
189 cmsg_type = IP_SENDSRCADDR
194 is defined to have the same value as
200 can be used directly as a control message for
206 option is enabled on a
210 socket, the destination address of outgoing
211 broadcast datagrams on that socket will be forced
212 to the undirected broadcast address,
213 .Dv INADDR_BROADCAST ,
215 This is in contrast to the default behavior of the
216 system, which is to transmit undirected broadcasts
217 via the first network interface with the
221 This option allows applications to choose which
222 interface is used to transmit an undirected broadcast
224 For example, the following code would force an
225 undirected broadcast to be transmitted via the interface
226 configured with the broadcast address 192.168.2.255:
229 struct sockaddr_in sin;
230 u_char onesbcast = 1; /* 0 = disable (default), 1 = enable */
232 setsockopt(s, IPPROTO_IP, IP_ONESBCAST, &onesbcast, sizeof(onesbcast));
233 sin.sin_addr.s_addr = inet_addr("192.168.2.255");
234 sin.sin_port = htons(1234);
235 sendto(s, msg, sizeof(msg), 0, &sin, sizeof(sin));
238 It is the application's responsibility to set the
241 to an appropriate value in order to prevent broadcast storms.
242 The application must have sufficient credentials to set the
244 socket level option, otherwise the
246 option has no effect.
250 option is enabled on a
257 to any address, even one not bound to any available network interface in the
259 This functionality (in conjunction with special firewall rules) can be used for
260 implementing a transparent proxy.
262 .Dv PRIV_NETINET_BINDANY
263 privilege is needed to set this option.
267 option is enabled on a
274 (time to live) field for a
277 The msg_control field in the msghdr structure points to a buffer
278 that contains a cmsghdr structure followed by the
280 The cmsghdr fields have the following values:
282 cmsg_len = CMSG_LEN(sizeof(u_char))
283 cmsg_level = IPPROTO_IP
284 cmsg_type = IP_RECVTTL
290 option is enabled on a
297 (type of service) field for a
300 The msg_control field in the msghdr structure points to a buffer
301 that contains a cmsghdr structure followed by the
303 The cmsghdr fields have the following values:
305 cmsg_len = CMSG_LEN(sizeof(u_char))
306 cmsg_level = IPPROTO_IP
307 cmsg_type = IP_RECVTOS
313 option is enabled on a
318 .Vt "struct sockaddr_dl"
319 corresponding to the interface on which the
325 structure points to a buffer that contains a
327 structure followed by the
328 .Vt "struct sockaddr_dl" .
331 fields have the following values:
333 cmsg_len = CMSG_LEN(sizeof(struct sockaddr_dl))
334 cmsg_level = IPPROTO_IP
335 cmsg_type = IP_RECVIF
339 may be used to set the port range used for selecting a local port number
340 on a socket with an unspecified (zero) port number.
343 .Bl -tag -width IP_PORTRANGE_DEFAULT
344 .It Dv IP_PORTRANGE_DEFAULT
345 use the default range of values, normally
346 .Dv IPPORT_HIFIRSTAUTO
348 .Dv IPPORT_HILASTAUTO .
349 This is adjustable through the sysctl setting:
350 .Va net.inet.ip.portrange.first
352 .Va net.inet.ip.portrange.last .
353 .It Dv IP_PORTRANGE_HIGH
354 use a high range of values, normally
355 .Dv IPPORT_HIFIRSTAUTO
357 .Dv IPPORT_HILASTAUTO .
358 This is adjustable through the sysctl setting:
359 .Va net.inet.ip.portrange.hifirst
361 .Va net.inet.ip.portrange.hilast .
362 .It Dv IP_PORTRANGE_LOW
363 use a low range of ports, which are normally restricted to
364 privileged processes on
367 The range is normally from
370 .Li IPPORT_RESERVEDSTART
372 This is adjustable through the sysctl setting:
373 .Va net.inet.ip.portrange.lowfirst
375 .Va net.inet.ip.portrange.lowlast .
378 The range of privileged ports which only may be opened by
379 root-owned processes may be modified by the
380 .Va net.inet.ip.portrange.reservedlow
382 .Va net.inet.ip.portrange.reservedhigh
384 The values default to the traditional range,
388 (0 through 1023), respectively.
389 Note that these settings do not affect and are not accounted for in the
390 use or calculation of the other
391 .Va net.inet.ip.portrange
393 Changing these values departs from
395 tradition and has security
396 consequences that the administrator should carefully evaluate before
397 modifying these settings.
399 Ports are allocated at random within the specified port range in order
400 to increase the difficulty of random spoofing attacks.
401 In scenarios such as benchmarking, this behavior may be undesirable.
403 .Va net.inet.ip.portrange.randomized
404 can be used to toggle randomization off.
406 .Va net.inet.ip.portrange.randomcps
407 ports have been allocated in the last second, then return to sequential
409 Return to random allocation only once the current port allocation rate
411 .Va net.inet.ip.portrange.randomcps
413 .Va net.inet.ip.portrange.randomtime
415 The default values for
416 .Va net.inet.ip.portrange.randomcps
418 .Va net.inet.ip.portrange.randomtime
419 are 10 port allocations per second and 45 seconds correspondingly.
420 .Ss "Multicast Options"
423 multicasting is supported only on
429 and only on networks where the interface
430 driver supports multicasting.
434 option changes the time-to-live (TTL)
435 for outgoing multicast datagrams
436 in order to control the scope of the multicasts:
438 u_char ttl; /* range: 0 to 255, default = 1 */
439 setsockopt(s, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
442 Datagrams with a TTL of 1 are not forwarded beyond the local network.
443 Multicast datagrams with a TTL of 0 will not be transmitted on any network,
444 but may be delivered locally if the sending host belongs to the destination
445 group and if multicast loopback has not been disabled on the sending socket
447 Multicast datagrams with TTL greater than 1 may be forwarded
448 to other networks if a multicast router is attached to the local network.
450 For hosts with multiple interfaces, where an interface has not
451 been specified for a multicast group membership,
452 each multicast transmission is sent from the primary network interface.
455 option overrides the default for
456 subsequent transmissions from a given socket:
459 setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF, &addr, sizeof(addr));
462 where "addr" is the local
464 address of the desired interface or
466 to specify the default interface.
468 To specify an interface by index, an instance of
470 may be passed instead.
473 member should be set to the index of the desired interface,
474 or 0 to specify the default interface.
475 The kernel differentiates between these two structures by their size.
480 .Em not recommended ,
481 as multicast memberships are scoped to each
482 individual interface.
483 It is supported for legacy use only by applications,
484 such as routing daemons, which expect to
485 be able to transmit link-local IPv4 multicast datagrams (224.0.0.0/24)
486 on multiple interfaces,
487 without requesting an individual membership for each interface.
490 An interface's local IP address and multicast capability can
496 Normal applications should not need to use this option.
498 If a multicast datagram is sent to a group to which the sending host itself
499 belongs (on the outgoing interface), a copy of the datagram is, by default,
500 looped back by the IP layer for local delivery.
502 .Dv IP_MULTICAST_LOOP
503 option gives the sender explicit control
504 over whether or not subsequent datagrams are looped back:
506 u_char loop; /* 0 = disable, 1 = enable (default) */
507 setsockopt(s, IPPROTO_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop));
511 improves performance for applications that may have no more than one
512 instance on a single host (such as a routing daemon), by eliminating
513 the overhead of receiving their own transmissions.
514 It should generally not
515 be used by applications for which there may be more than one instance on a
516 single host (such as a conferencing program) or for which the sender does
517 not belong to the destination group (such as a time querying program).
520 .Va net.inet.ip.mcast.loop
521 controls the default setting of the
522 .Dv IP_MULTICAST_LOOP
523 socket option for new sockets.
525 A multicast datagram sent with an initial TTL greater than 1 may be delivered
526 to the sending host on a different interface from that on which it was sent,
527 if the host belongs to the destination group on that other interface.
528 The loopback control option has no effect on such delivery.
530 A host must become a member of a multicast group before it can receive
531 datagrams sent to the group.
532 To join a multicast group, use the
533 .Dv IP_ADD_MEMBERSHIP
537 setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));
542 is the following structure:
545 struct in_addr imr_multiaddr; /* IP multicast address of group */
546 struct in_addr imr_interface; /* local IP address of interface */
553 address of a particular multicast-capable interface if
554 the host is multihomed.
557 to choose the default interface, although this is not recommended;
558 this is considered to be the first interface corresponding
559 to the default route.
560 Otherwise, the first multicast-capable interface
561 configured in the system will be used.
567 member is within the network range
569 it is treated as an interface index in the system interface MIB,
570 as per the RIP Version 2 MIB Extension (RFC-1724).
573 since 7.0, this behavior is no longer supported.
575 instead use the RFC 3678 multicast source filter APIs; in particular,
576 .Dv MCAST_JOIN_GROUP .
579 .Dv IP_MAX_MEMBERSHIPS
580 memberships may be added on a single socket.
581 Membership is associated with a single interface;
582 programs running on multihomed hosts may need to
583 join the same group on more than one interface.
585 To drop a membership, use:
588 setsockopt(s, IPPROTO_IP, IP_DROP_MEMBERSHIP, &mreq, sizeof(mreq));
593 contains the same values as used to add the membership.
594 Memberships are dropped when the socket is closed or the process exits.
595 .\" TODO: Update this piece when IPv4 source-address selection is implemented.
597 The IGMP protocol uses the primary IP address of the interface
598 as its identifier for group membership.
599 This is the first IP address configured on the interface.
600 If this address is removed or changed, the results are
601 undefined, as the IGMP membership state will then be inconsistent.
602 If multiple IP aliases are configured on the same interface,
603 they will be ignored.
605 This shortcoming was addressed in IPv6; MLDv2 requires
606 that the unique link-local address for an interface is
607 used to identify an MLDv2 listener.
608 .Ss "Source-Specific Multicast Options"
611 the use of Source-Specific Multicast (SSM) is supported.
612 These extensions require an IGMPv3 multicast router in order to
613 make best use of them.
614 If a legacy multicast router is present on the link,
616 will simply downgrade to the version of IGMP spoken by the router,
617 and the benefits of source filtering on the upstream link
618 will not be present, although the kernel will continue to
619 squelch transmissions from blocked sources.
621 Each group membership on a socket now has a filter mode:
622 .Bl -tag -width MCAST_EXCLUDE
624 Datagrams sent to this group are accepted,
625 unless the source is in a list of blocked source addresses.
627 Datagrams sent to this group are accepted
628 only if the source is in a list of accepted source addresses.
631 Groups joined using the legacy
632 .Dv IP_ADD_MEMBERSHIP
633 option are placed in exclusive-mode,
634 and are able to request that certain sources are blocked or allowed.
636 .Em delta-based API .
638 To block a multicast source on an existing group membership:
640 struct ip_mreq_source mreqs;
641 setsockopt(s, IPPROTO_IP, IP_BLOCK_SOURCE, &mreqs, sizeof(mreqs));
646 is the following structure:
648 struct ip_mreq_source {
649 struct in_addr imr_multiaddr; /* IP multicast address of group */
650 struct in_addr imr_sourceaddr; /* IP address of source */
651 struct in_addr imr_interface; /* local IP address of interface */
655 should be set to the address of the source to be blocked.
657 To unblock a multicast source on an existing group:
659 struct ip_mreq_source mreqs;
660 setsockopt(s, IPPROTO_IP, IP_UNBLOCK_SOURCE, &mreqs, sizeof(mreqs));
666 .Dv IP_UNBLOCK_SOURCE
669 for inclusive-mode group memberships.
671 To join a multicast group in
673 mode with a single source,
674 or add another source to an existing inclusive-mode membership:
676 struct ip_mreq_source mreqs;
677 setsockopt(s, IPPROTO_IP, IP_ADD_SOURCE_MEMBERSHIP, &mreqs, sizeof(mreqs));
680 To leave a single source from an existing group in inclusive mode:
682 struct ip_mreq_source mreqs;
683 setsockopt(s, IPPROTO_IP, IP_DROP_SOURCE_MEMBERSHIP, &mreqs, sizeof(mreqs));
685 If this is the last accepted source for the group, the membership
689 .Dv IP_ADD_SOURCE_MEMBERSHIP
691 .Dv IP_DROP_SOURCE_MEMBERSHIP
694 for exclusive-mode group memberships.
695 However, both exclusive and inclusive mode memberships
696 support the use of the
698 documented in RFC 3678.
699 For management of source filter lists using this API,
704 .Va net.inet.ip.mcast.maxsocksrc
706 .Va net.inet.ip.mcast.maxgrpsrc
707 are used to specify an upper limit on the number of per-socket and per-group
708 source filter entries which the kernel may allocate.
709 .\"-----------------------
714 sockets are connectionless,
715 and are normally used with the
721 call may also be used to fix the destination for future
722 packets (in which case the
730 system calls may be used).
734 is 0, the default protocol
737 packets, and only incoming packets destined for that protocol
741 is non-zero, that protocol number will be used on outgoing packets
742 and to filter incoming packets.
744 Outgoing packets automatically have an
747 them (based on the destination address and the protocol
748 number the socket is created with),
752 Incoming packets are received with
754 header and options intact.
757 indicates the complete IP header is included with the data
758 and may be used only with the
762 #include <netinet/in_systm.h>
763 #include <netinet/ip.h>
765 int hincl = 1; /* 1 = on, 0 = off */
766 setsockopt(s, IPPROTO_IP, IP_HDRINCL, &hincl, sizeof(hincl));
771 releases, the program must set all
772 the fields of the IP header, including the following:
774 ip->ip_v = IPVERSION;
775 ip->ip_hl = hlen >> 2;
776 ip->ip_id = 0; /* 0 means kernel set appropriate value */
786 be provided in host byte order .
787 All other fields must be provided in network byte order.
790 for more information on network byte order.
793 field is set to 0 then the kernel will choose an
795 If the header source address is set to
797 the kernel will choose an appropriate address.
799 A socket operation may fail with one of the following errors returned:
802 when trying to establish a connection on a socket which
803 already has one, or when trying to send a datagram with the destination
804 address specified and the socket is already connected;
806 when trying to send a datagram, but
807 no destination address is specified, and the socket has not been
810 when the system runs out of memory for
811 an internal data structure;
812 .It Bq Er EADDRNOTAVAIL
813 when an attempt is made to create a
814 socket with a network address for which no network interface
817 when an attempt is made to create
818 a raw IP socket by a non-privileged process.
821 The following errors specific to
823 may occur when setting or getting
828 An unknown socket option name was given.
830 The IP option field was improperly formed;
831 an option field was shorter than the minimum value
832 or longer than the option buffer provided.
835 The following errors may occur when attempting to send
846 field was not equal to the length of the datagram written to the socket.
863 .%T "Socket Interface Extensions for Multicast Source Filters"
874 structure appeared in
projects / FreeBSD / stable / 8.git / blob