1 .\" $KAME: ip6.4,v 1.23 2005/01/11 05:56:25 itojun Exp $
2 .\" $OpenBSD: ip6.4,v 1.21 2005/01/06 03:50:46 itojun Exp $
3 .\" $FreeBSD: src/share/man/man4/ip6.4,v 1.18 2005/01/23 16:02:48 gnn Exp $
4 .\" $DragonFly: src/share/man/man4/ip6.4,v 1.3 2005/01/23 17:03:13 hrs Exp $
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37 .Nd Internet Protocol version 6 (IPv6) network layer
42 .Fn socket AF_INET6 SOCK_RAW proto
44 The IPv6 network layer is used by the IPv6 protocol family for
46 IPv6 packets contain an IPv6 header that is not provided as part of the
47 payload contents when passed to an application.
48 IPv6 header options affect the behavior of this protocol and may be used
49 by high-level protocols (such as the
53 protocols) as well as directly by
55 which process IPv6 messages at a lower-level and may be useful for
56 developing new protocols and special-purpose applications.
58 All IPv6 packets begin with an IPv6 header.
59 When data received by the kernel are passed to the application, this
60 header is not included in buffer, even when raw sockets are being used.
61 Likewise, when data are sent to the kernel for transmit from the
62 application, the buffer is not examined for an IPv6 header:
63 the kernel always constructs the header.
64 To directly access IPv6 headers from received packets and specify them
65 as part of the buffer passed to the kernel, link-level access
70 must instead be utilized.
72 The header has the following definition:
73 .Bd -literal -offset indent
77 u_int32_t ip6_un1_flow; /* 20 bits of flow ID */
78 u_int16_t ip6_un1_plen; /* payload length */
79 u_int8_t ip6_un1_nxt; /* next header */
80 u_int8_t ip6_un1_hlim; /* hop limit */
82 u_int8_t ip6_un2_vfc; /* version and class */
84 struct in6_addr ip6_src; /* source address */
85 struct in6_addr ip6_dst; /* destination address */
88 #define ip6_vfc ip6_ctlun.ip6_un2_vfc
89 #define ip6_flow ip6_ctlun.ip6_un1.ip6_un1_flow
90 #define ip6_plen ip6_ctlun.ip6_un1.ip6_un1_plen
91 #define ip6_nxt ip6_ctlun.ip6_un1.ip6_un1_nxt
92 #define ip6_hlim ip6_ctlun.ip6_un1.ip6_un1_hlim
93 #define ip6_hops ip6_ctlun.ip6_un1.ip6_un1_hlim
96 All fields are in network-byte order.
97 Any options specified (see
99 below) must also be specified in network-byte order.
102 specifies the flow ID.
104 specifies the payload length.
106 specifies the type of the next header.
108 specifies the hop limit.
112 specify the class and the bottom 4 bits specify the version.
117 specify the source and destination addresses.
119 The IPv6 header may be followed by any number of extension headers that start
120 with the following generic definition:
121 .Bd -literal -offset indent
128 IPv6 allows header options on packets to manipulate the behavior of the
130 These options and other control requests are accessed with the
134 system calls at level
136 and by using ancillary data in
140 They can be used to access most of the fields in the IPv6 header and
143 The following socket options are supported:
145 .\" .It Dv IPV6_OPTIONS
146 .It Dv IPV6_UNICAST_HOPS Fa "int *"
147 Get or set the default hop limit header field for outgoing unicast
148 datagrams sent on this socket.
149 A value of \-1 resets to the default value.
150 .\" .It Dv IPV6_RECVOPTS Fa "int *"
151 .\" Get or set the status of whether all header options will be
152 .\" delivered along with the datagram when it is received.
153 .\" .It Dv IPV6_RECVRETOPTS Fa "int *"
154 .\" Get or set the status of whether header options will be delivered
156 .\" .It Dv IPV6_RECVDSTADDR Fa "int *"
157 .\" Get or set the status of whether datagrams are received with
158 .\" destination addresses.
159 .\" .It Dv IPV6_RETOPTS
160 .\" Get or set IPv6 options.
161 .It Dv IPV6_MULTICAST_IF Fa "u_int *"
162 Get or set the interface from which multicast packets will be sent.
163 For hosts with multiple interfaces, each multicast transmission is sent
164 from the primary network interface.
165 The interface is specified as its index as provided by
166 .Xr if_nametoindex 3 .
167 A value of zero specifies the default interface.
168 .It Dv IPV6_MULTICAST_HOPS Fa "int *"
169 Get or set the default hop limit header field for outgoing multicast
170 datagrams sent on this socket.
171 This option controls the scope of multicast datagram transmissions.
173 Datagrams with a hop limit of 1 are not forwarded beyond the local
175 Multicast datagrams with a hop limit of zero will not be transmitted on
176 any network but may be delivered locally if the sending host belongs to
177 the destination group and if multicast loopback (see below) has not been
178 disabled on the sending socket.
179 Multicast datagrams with a hop limit greater than 1 may be forwarded to
180 the other networks if a multicast router (such as
182 is attached to the local network.
183 .It Dv IPV6_MULTICAST_LOOP Fa "u_int *"
184 Get or set the status of whether multicast datagrams will be looped back
185 for local delivery when a multicast datagram is sent to a group to which
186 the sending host belongs.
188 This option improves performance for applications that may have no more
189 than one instance on a single host (such as a router daemon) by
190 eliminating the overhead of receiving their own transmissions.
191 It should generally not be used by applications for which there may be
192 more than one instance on a single host (such as a conferencing program)
193 or for which the sender does not belong to the destination group
194 (such as a time-querying program).
196 A multicast datagram sent with an initial hop limit greater than 1 may
197 be delivered to the sending host on a different interface from that on
198 which it was sent if the host belongs to the destination group on that
200 The multicast loopback control option has no effect on such delivery.
201 .It Dv IPV6_JOIN_GROUP Fa "struct ipv6_mreq *"
202 Join a multicast group.
203 A host must become a member of a multicast group before it can receive
204 datagrams sent to the group.
207 struct in6_addr ipv6mr_multiaddr;
208 unsigned int ipv6mr_interface;
213 may be set to zeroes to choose the default multicast interface or to the
214 index of a particular multicast-capable interface if the host is
216 Membership is associated with a single interface; programs running on
217 multihomed hosts may need to join the same group on more than one
220 If the multicast address is unspecified (i.e., all zeroes), messages
221 from all multicast addresses will be accepted by this group.
222 Note that setting to this value requires superuser privileges.
223 .It Dv IPV6_LEAVE_GROUP Fa "struct ipv6_mreq *"
224 Drop membership from the associated multicast group.
225 Memberships are automatically dropped when the socket is closed or when
227 .It Dv IPV6_PORTRANGE Fa "int *"
228 Get or set the allocation policy of ephemeral ports for when the kernel
229 automatically binds a local address to this socket.
230 The following values are available:
232 .Bl -tag -width IPV6_PORTRANGE_DEFAULT -compact
233 .It Dv IPV6_PORTRANGE_DEFAULT
234 Use the regular range of non-reserved ports (varies, see
236 .It Dv IPV6_PORTRANGE_HIGH
237 Use a high range (varies, see
239 .It Dv IPV6_PORTRANGE_LOW
240 Use a low, reserved range (600\-1023).
242 .It Dv IPV6_PKTINFO Fa "int *"
243 Get or set whether additional information about subsequent packets will
244 be provided as ancillary data along with the payload in subsequent
247 The information is stored in the following structure in the ancillary
251 struct in6_addr ipi6_addr; /* src/dst IPv6 address */
252 unsigned int ipi6_ifindex; /* send/recv if index */
255 .It Dv IPV6_HOPLIMIT Fa "int *"
256 Get or set whether the hop limit header field from subsequent packets
257 will be provided as ancillary data along with the payload in subsequent
260 The value is stored as an
262 in the ancillary data returned.
263 .\" .It Dv IPV6_NEXTHOP Fa "int *"
264 .\" Get or set whether the address of the next hop for subsequent
265 .\" packets will be provided as ancillary data along with the payload in
269 .\" The option is stored as a
271 .\" structure in the ancillary data returned.
273 .\" This option requires superuser privileges.
274 .It Dv IPV6_HOPOPTS Fa "int *"
275 Get or set whether the hop-by-hop options from subsequent packets will be
276 provided as ancillary data along with the payload in subsequent
279 The option is stored in the following structure in the ancillary data
283 u_int8_t ip6h_nxt; /* next header */
284 u_int8_t ip6h_len; /* length in units of 8 octets */
285 /* followed by options */
290 .Fn inet6_option_space
291 routine and family of routines may be used to manipulate this data.
293 This option requires superuser privileges.
294 .It Dv IPV6_DSTOPTS Fa "int *"
295 Get or set whether the destination options from subsequent packets will
296 be provided as ancillary data along with the payload in subsequent
299 The option is stored in the following structure in the ancillary data
303 u_int8_t ip6d_nxt; /* next header */
304 u_int8_t ip6d_len; /* length in units of 8 octets */
305 /* followed by options */
310 .Fn inet6_option_space
311 routine and family of routines may be used to manipulate this data.
313 This option requires superuser privileges.
314 .It Dv IPV6_RTHDR Fa "int *"
315 Get or set whether the routing header from subsequent packets will be
316 provided as ancillary data along with the payload in subsequent
319 The header is stored in the following structure in the ancillary data
323 u_int8_t ip6r_nxt; /* next header */
324 u_int8_t ip6r_len; /* length in units of 8 octets */
325 u_int8_t ip6r_type; /* routing type */
326 u_int8_t ip6r_segleft; /* segments left */
327 /* followed by routing-type-specific data */
332 .Fn inet6_option_space
333 routine and family of routines may be used to manipulate this data.
335 This option requires superuser privileges.
336 .It Dv IPV6_PKTOPTIONS Fa "struct cmsghdr *"
337 Get or set all header options and extension headers at one time on the
338 last packet sent or received on the socket.
339 All options must fit within the size of an mbuf (see
341 Options are specified as a series of
343 structures followed by corresponding values.
348 to one of the other values in this list, and trailing data to the option
350 When setting options, if the length
354 is zero, all header options will be reset to their default values.
355 Otherwise, the length should specify the size the series of control
360 to specify option values, the ancillary data used in these calls that
361 correspond to the desired header options may be directly specified as
362 the control message in the series of control messages provided as the
365 .It Dv IPV6_CHECKSUM Fa "int *"
366 Get or set the byte offset into a packet where the 16-bit checksum is
368 When set, this byte offset is where incoming packets will be expected
369 to have checksums of their data stored and where outgoing packets will
370 have checksums of their data computed and stored by the kernel.
371 A value of \-1 specifies that no checksums will be checked on incoming
372 packets and that no checksums will be computed or stored on outgoing
374 The offset of the checksum for ICMPv6 sockets cannot be relocated or
376 .It Dv IPV6_V6ONLY Fa "int *"
377 Get or set whether only IPv6 connections can be made to this socket.
378 For wildcard sockets, this can restrict connections to IPv6 only.
381 .\"IPv6 sockets are always IPv6-only, so the socket option is read-only
383 .It Dv IPV6_FAITH Fa "int *"
384 Get or set the status of whether
386 connections can be made to this socket.
387 .It Dv IPV6_USE_MIN_MTU Fa "int *"
388 Get or set whether the minimal IPv6 maximum transmission unit (MTU) size
389 will be used to avoid fragmentation from occurring for subsequent
391 .It Dv IPV6_AUTH_LEVEL Fa "int *"
394 authentication level.
395 .It Dv IPV6_ESP_TRANS_LEVEL Fa "int *"
396 Get or set the ESP transport level.
397 .It Dv IPV6_ESP_NETWORK_LEVEL Fa "int *"
398 Get or set the ESP encapsulation level.
399 .It Dv IPV6_IPCOMP_LEVEL Fa "int *"
407 .\" .Dv IPV6_NEXTHOP ,
413 options will return ancillary data along with payload contents in subsequent
421 set to respective option name value (e.g.,
422 .Dv IPV6_HOPTLIMIT ) .
423 These options may also be used directly as ancillary
427 to set options on the packet being transmitted by the call.
432 For these options, the ancillary data object value format is the same
433 as the value returned as explained for each when received with
438 to specify options on particular packets works only on UDP and raw sockets.
439 To manipulate header options for packets on TCP sockets, only the socket
442 In some cases, there are multiple APIs defined for manipulating an IPv6
444 A good example is the outgoing interface for multicast datagrams, which
446 .Dv IPV6_MULTICAST_IF
447 socket option, through the
449 option, and through the
451 field of the socket address passed to the
455 Resolving these conflicts is implementation dependent.
456 This implementation determines the value in the following way:
457 options specified by using ancillary data (i.e.,
459 are considered first,
460 options specified by using
464 options are considered second,
465 options specified by using the individual, basic, and direct socket
467 .Dv IPV6_UNICAST_HOPS )
468 are considered third,
469 and options specified in the socket address supplied to
473 IPv6 multicasting is supported only on
479 and only on networks where the interface driver supports
481 Socket options (see above) that manipulate membership of
482 multicast groups and other multicast options include
483 .Dv IPV6_MULTICAST_IF ,
484 .Dv IPV6_MULTICAST_HOPS ,
485 .Dv IPV6_MULTICAST_LOOP ,
486 .Dv IPV6_LEAVE_GROUP ,
488 .Dv IPV6_JOIN_GROUP .
490 Raw IPv6 sockets are connectionless and are normally used with the
496 call may be used to fix the destination address for future outgoing
499 may instead be used and the
501 call may be used to fix the source address for future outgoing
502 packets instead of having the kernel choose a source address.
508 raw socket input is constrained to only packets with their
509 source address matching the socket destination address if
511 was used and to packets with their destination address
512 matching the socket source address if
520 is zero, the default protocol
522 is used for outgoing packets.
523 For incoming packets, protocols recognized by kernel are
525 passed to the application socket (e.g.,
529 except for some ICMPv6 messages.
530 The ICMPv6 messages not passed to raw sockets include echo, timestamp,
531 and address mask requests.
534 is non-zero, only packets with this protocol will be passed to the
537 IPv6 fragments are also not passed to application sockets until
538 they have been reassembled.
539 If reception of all packets is desired, link-level access (such as
541 must be used instead.
543 Outgoing packets automatically have an IPv6 header prepended to them
544 (based on the destination address and the protocol number the socket
546 Incoming packets are received by an application without the IPv6 header
547 or any extension headers.
549 Outgoing packets will be fragmented automatically by the kernel if they
551 Incoming packets will be reassembled before being sent to the raw socket,
552 so packet fragments or fragment headers will never be seen on a raw socket.
554 The following determines the hop limit on the next packet received:
565 (void)memset(&m, 0, sizeof(m));
566 (void)memset(&iov, 0, sizeof(iov));
568 iov[0].iov_base = data; /* buffer for packet payload */
569 iov[0].iov_len = sizeof(data); /* expected packet length */
571 m.msg_name = &from; /* sockaddr_in6 of peer */
572 m.msg_namelen = sizeof(from);
575 m.msg_control = (caddr_t)buf; /* buffer for control messages */
576 m.msg_controllen = sizeof(buf);
579 * Enable the hop limit value from received packets to be
580 * returned along with the payload.
583 if (setsockopt(s, IPPROTO_IPV6, IPV6_HOPLIMIT, &optval,
584 sizeof(optval)) == -1)
585 err(1, "setsockopt");
589 if (recvmsg(s, &m, 0) == -1)
591 for (cm = CMSG_FIRSTHDR(&m); cm != NULL;
592 cm = CMSG_NXTHDR(&m, cm)) {
593 if (cm->cmsg_level == IPPROTO_IPV6 &&
594 cm->cmsg_type == IPV6_HOPLIMIT &&
595 cm->cmsg_len == CMSG_LEN(sizeof(int))) {
597 (void)printf("hop limit: %d\en",
598 *(int *)CMSG_DATA(cm));
605 A socket operation may fail with one of the following errors returned:
606 .Bl -tag -width EADDRNOTAVAILxx
608 when trying to establish a connection on a socket which
609 already has one or when trying to send a datagram with the destination
610 address specified and the socket is already connected.
612 when trying to send a datagram, but
613 no destination address is specified, and the socket hasn't been
616 when the system runs out of memory for
617 an internal data structure.
618 .It Bq Er EADDRNOTAVAIL
619 when an attempt is made to create a
620 socket with a network address for which no network interface
623 when an attempt is made to create
624 a raw IPv6 socket by a non-privileged process.
627 The following errors specific to IPv6 may occur when setting or getting
629 .Bl -tag -width EADDRNOTAVAILxx
631 An unknown socket option name was given.
633 An ancillary data object was improperly formed.
641 .\" .Xr inet6_option_space 3 ,
642 .\" .Xr inet6_rthdr_space 3 ,
643 .Xr if_nametoindex 3 ,
653 .%T Advanced Sockets API for IPv6
660 .%T Internet Protocol, Version 6 (IPv6) Specification
669 .%T Basic Socket Interface Extensions for IPv6
677 .%T UNIX Network Programming, third edition
680 Most of the socket options are defined in RFC 2292 or RFC 2553.
683 socket option is defined in RFC 3542.
686 socket option and the conflict resolution rule are not defined in the
687 RFCs and should be considered implementation dependent.