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 $
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38 .Nd Internet Protocol version 6 (IPv6) network layer
43 .Fn socket AF_INET6 SOCK_RAW proto
45 The IPv6 network layer is used by the IPv6 protocol family for
47 IPv6 packets contain an IPv6 header that is not provided as part of the
48 payload contents when passed to an application.
49 IPv6 header options affect the behavior of this protocol and may be used
50 by high-level protocols (such as the
54 protocols) as well as directly by
56 which process IPv6 messages at a lower-level and may be useful for
57 developing new protocols and special-purpose applications.
59 All IPv6 packets begin with an IPv6 header.
60 When data received by the kernel are passed to the application, this
61 header is not included in buffer, even when raw sockets are being used.
62 Likewise, when data are sent to the kernel for transmit from the
63 application, the buffer is not examined for an IPv6 header:
64 the kernel always constructs the header.
65 To directly access IPv6 headers from received packets and specify them
66 as part of the buffer passed to the kernel, link-level access
71 must instead be utilized.
73 The header has the following definition:
74 .Bd -literal -offset indent
78 u_int32_t ip6_un1_flow; /* 20 bits of flow ID */
79 u_int16_t ip6_un1_plen; /* payload length */
80 u_int8_t ip6_un1_nxt; /* next header */
81 u_int8_t ip6_un1_hlim; /* hop limit */
83 u_int8_t ip6_un2_vfc; /* version and class */
85 struct in6_addr ip6_src; /* source address */
86 struct in6_addr ip6_dst; /* destination address */
89 #define ip6_vfc ip6_ctlun.ip6_un2_vfc
90 #define ip6_flow ip6_ctlun.ip6_un1.ip6_un1_flow
91 #define ip6_plen ip6_ctlun.ip6_un1.ip6_un1_plen
92 #define ip6_nxt ip6_ctlun.ip6_un1.ip6_un1_nxt
93 #define ip6_hlim ip6_ctlun.ip6_un1.ip6_un1_hlim
94 #define ip6_hops ip6_ctlun.ip6_un1.ip6_un1_hlim
97 All fields are in network-byte order.
98 Any options specified (see
100 below) must also be specified in network-byte order.
103 specifies the flow ID.
105 specifies the payload length.
107 specifies the type of the next header.
109 specifies the hop limit.
113 specify the class and the bottom 4 bits specify the version.
118 specify the source and destination addresses.
120 The IPv6 header may be followed by any number of extension headers that start
121 with the following generic definition:
122 .Bd -literal -offset indent
129 IPv6 allows header options on packets to manipulate the behavior of the
131 These options and other control requests are accessed with the
135 system calls at level
137 and by using ancillary data in
141 They can be used to access most of the fields in the IPv6 header and
144 The following socket options are supported:
146 .\" .It Dv IPV6_OPTIONS
147 .It Dv IPV6_UNICAST_HOPS Fa "int *"
148 Get or set the default hop limit header field for outgoing unicast
149 datagrams sent on this socket.
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
181 .Xr mrouted 8 Pq Pa ports/net/mrouted )
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_TCLASS Fa "int *"
315 Get or set the value of the traffic class field used for outgoing datagrams
317 The value must be between \-1 and 255.
318 A value of \-1 resets to the default value.
319 .It Dv IPV6_RECVTCLASS Fa "int *"
320 Get or set the status of whether the traffic class header field will be
321 provided as ancillary data along with the payload in subsequent
324 The header field is stored as a single value of type
326 .It Dv IPV6_RTHDR Fa "int *"
327 Get or set whether the routing header from subsequent packets will be
328 provided as ancillary data along with the payload in subsequent
331 The header is stored in the following structure in the ancillary data
335 u_int8_t ip6r_nxt; /* next header */
336 u_int8_t ip6r_len; /* length in units of 8 octets */
337 u_int8_t ip6r_type; /* routing type */
338 u_int8_t ip6r_segleft; /* segments left */
339 /* followed by routing-type-specific data */
344 .Fn inet6_option_space
345 routine and family of routines may be used to manipulate this data.
347 This option requires superuser privileges.
348 .It Dv IPV6_PKTOPTIONS Fa "struct cmsghdr *"
349 Get or set all header options and extension headers at one time on the
350 last packet sent or received on the socket.
351 All options must fit within the size of an mbuf (see
353 Options are specified as a series of
355 structures followed by corresponding values.
360 to one of the other values in this list, and trailing data to the option
362 When setting options, if the length
366 is zero, all header options will be reset to their default values.
367 Otherwise, the length should specify the size the series of control
372 to specify option values, the ancillary data used in these calls that
373 correspond to the desired header options may be directly specified as
374 the control message in the series of control messages provided as the
377 .It Dv IPV6_CHECKSUM Fa "int *"
378 Get or set the byte offset into a packet where the 16-bit checksum is
380 When set, this byte offset is where incoming packets will be expected
381 to have checksums of their data stored and where outgoing packets will
382 have checksums of their data computed and stored by the kernel.
383 A value of \-1 specifies that no checksums will be checked on incoming
384 packets and that no checksums will be computed or stored on outgoing
386 The offset of the checksum for ICMPv6 sockets cannot be relocated or
388 .It Dv IPV6_V6ONLY Fa "int *"
389 Get or set whether only IPv6 connections can be made to this socket.
390 For wildcard sockets, this can restrict connections to IPv6 only.
393 .\"IPv6 sockets are always IPv6-only, so the socket option is read-only
395 .It Dv IPV6_FAITH Fa "int *"
396 Get or set the status of whether
398 connections can be made to this socket.
399 .It Dv IPV6_USE_MIN_MTU Fa "int *"
400 Get or set whether the minimal IPv6 maximum transmission unit (MTU) size
401 will be used to avoid fragmentation from occurring for subsequent
403 .It Dv IPV6_AUTH_LEVEL Fa "int *"
406 authentication level.
407 .It Dv IPV6_ESP_TRANS_LEVEL Fa "int *"
408 Get or set the ESP transport level.
409 .It Dv IPV6_ESP_NETWORK_LEVEL Fa "int *"
410 Get or set the ESP encapsulation level.
411 .It Dv IPV6_IPCOMP_LEVEL Fa "int *"
419 .\" .Dv IPV6_NEXTHOP ,
425 options will return ancillary data along with payload contents in subsequent
433 set to respective option name value (e.g.,
434 .Dv IPV6_HOPTLIMIT ) .
435 These options may also be used directly as ancillary
439 to set options on the packet being transmitted by the call.
444 For these options, the ancillary data object value format is the same
445 as the value returned as explained for each when received with
450 to specify options on particular packets works only on UDP and raw sockets.
451 To manipulate header options for packets on TCP sockets, only the socket
454 In some cases, there are multiple APIs defined for manipulating an IPv6
456 A good example is the outgoing interface for multicast datagrams, which
458 .Dv IPV6_MULTICAST_IF
459 socket option, through the
461 option, and through the
463 field of the socket address passed to the
467 Resolving these conflicts is implementation dependent.
468 This implementation determines the value in the following way:
469 options specified by using ancillary data (i.e.,
471 are considered first,
472 options specified by using
476 options are considered second,
477 options specified by using the individual, basic, and direct socket
479 .Dv IPV6_UNICAST_HOPS )
480 are considered third,
481 and options specified in the socket address supplied to
485 IPv6 multicasting is supported only on
491 and only on networks where the interface driver supports
493 Socket options (see above) that manipulate membership of
494 multicast groups and other multicast options include
495 .Dv IPV6_MULTICAST_IF ,
496 .Dv IPV6_MULTICAST_HOPS ,
497 .Dv IPV6_MULTICAST_LOOP ,
498 .Dv IPV6_LEAVE_GROUP ,
500 .Dv IPV6_JOIN_GROUP .
502 Raw IPv6 sockets are connectionless and are normally used with the
508 call may be used to fix the destination address for future outgoing
511 may instead be used and the
513 call may be used to fix the source address for future outgoing
514 packets instead of having the kernel choose a source address.
520 raw socket input is constrained to only packets with their
521 source address matching the socket destination address if
523 was used and to packets with their destination address
524 matching the socket source address if
532 is zero, the default protocol
534 is used for outgoing packets.
535 For incoming packets, protocols recognized by kernel are
537 passed to the application socket (e.g.,
541 except for some ICMPv6 messages.
542 The ICMPv6 messages not passed to raw sockets include echo, timestamp,
543 and address mask requests.
546 is non-zero, only packets with this protocol will be passed to the
549 IPv6 fragments are also not passed to application sockets until
550 they have been reassembled.
551 If reception of all packets is desired, link-level access (such as
553 must be used instead.
555 Outgoing packets automatically have an IPv6 header prepended to them
556 (based on the destination address and the protocol number the socket
558 Incoming packets are received by an application without the IPv6 header
559 or any extension headers.
561 Outgoing packets will be fragmented automatically by the kernel if they
563 Incoming packets will be reassembled before being sent to the raw socket,
564 so packet fragments or fragment headers will never be seen on a raw socket.
566 The following determines the hop limit on the next packet received:
577 (void)memset(&m, 0, sizeof(m));
578 (void)memset(&iov, 0, sizeof(iov));
580 iov[0].iov_base = data; /* buffer for packet payload */
581 iov[0].iov_len = sizeof(data); /* expected packet length */
583 m.msg_name = &from; /* sockaddr_in6 of peer */
584 m.msg_namelen = sizeof(from);
587 m.msg_control = (caddr_t)buf; /* buffer for control messages */
588 m.msg_controllen = sizeof(buf);
591 * Enable the hop limit value from received packets to be
592 * returned along with the payload.
595 if (setsockopt(s, IPPROTO_IPV6, IPV6_HOPLIMIT, &optval,
596 sizeof(optval)) == -1)
597 err(1, "setsockopt");
601 if (recvmsg(s, &m, 0) == -1)
603 for (cm = CMSG_FIRSTHDR(&m); cm != NULL;
604 cm = CMSG_NXTHDR(&m, cm)) {
605 if (cm->cmsg_level == IPPROTO_IPV6 &&
606 cm->cmsg_type == IPV6_HOPLIMIT &&
607 cm->cmsg_len == CMSG_LEN(sizeof(int))) {
609 (void)printf("hop limit: %d\en",
610 *(int *)CMSG_DATA(cm));
617 A socket operation may fail with one of the following errors returned:
618 .Bl -tag -width EADDRNOTAVAILxx
620 when trying to establish a connection on a socket which
621 already has one or when trying to send a datagram with the destination
622 address specified and the socket is already connected.
624 when trying to send a datagram, but
625 no destination address is specified, and the socket has not been
628 when the system runs out of memory for
629 an internal data structure.
630 .It Bq Er EADDRNOTAVAIL
631 when an attempt is made to create a
632 socket with a network address for which no network interface
635 when an attempt is made to create
636 a raw IPv6 socket by a non-privileged process.
639 The following errors specific to IPv6 may occur when setting or getting
641 .Bl -tag -width EADDRNOTAVAILxx
643 An unknown socket option name was given.
645 An ancillary data object was improperly formed.
653 .\" .Xr inet6_option_space 3 ,
654 .\" .Xr inet6_rthdr_space 3 ,
655 .Xr if_nametoindex 3 ,
665 .%T Advanced Sockets API for IPv6
672 .%T Internet Protocol, Version 6 (IPv6) Specification
681 .%T Basic Socket Interface Extensions for IPv6
689 .%T UNIX Network Programming, third edition
692 Most of the socket options are defined in RFC 2292 or RFC 2553.
695 socket option is defined in RFC 3542.
698 socket option and the conflict resolution rule are not defined in the
699 RFCs and should be considered implementation dependent.