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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36 .Nd Internet Protocol version 6 (IPv6) network layer
41 .Fn socket AF_INET6 SOCK_RAW proto
43 The IPv6 network layer is used by the IPv6 protocol family for
45 IPv6 packets contain an IPv6 header that is not provided as part of the
46 payload contents when passed to an application.
47 IPv6 header options affect the behavior of this protocol and may be used
48 by high-level protocols (such as the
52 protocols) as well as directly by
54 which process IPv6 messages at a lower-level and may be useful for
55 developing new protocols and special-purpose applications.
57 All IPv6 packets begin with an IPv6 header.
58 When data received by the kernel are passed to the application, this
59 header is not included in buffer, even when raw sockets are being used.
60 Likewise, when data are sent to the kernel for transmit from the
61 application, the buffer is not examined for an IPv6 header:
62 the kernel always constructs the header.
63 To directly access IPv6 headers from received packets and specify them
64 as part of the buffer passed to the kernel, link-level access
69 must instead be utilized.
71 The header has the following definition:
72 .Bd -literal -offset indent
76 uint32_t ip6_un1_flow; /* 20 bits of flow ID */
77 uint16_t ip6_un1_plen; /* payload length */
78 uint8_t ip6_un1_nxt; /* next header */
79 uint8_t ip6_un1_hlim; /* hop limit */
81 uint8_t ip6_un2_vfc; /* version and class */
83 struct in6_addr ip6_src; /* source address */
84 struct in6_addr ip6_dst; /* destination address */
87 #define ip6_vfc ip6_ctlun.ip6_un2_vfc
88 #define ip6_flow ip6_ctlun.ip6_un1.ip6_un1_flow
89 #define ip6_plen ip6_ctlun.ip6_un1.ip6_un1_plen
90 #define ip6_nxt ip6_ctlun.ip6_un1.ip6_un1_nxt
91 #define ip6_hlim ip6_ctlun.ip6_un1.ip6_un1_hlim
92 #define ip6_hops ip6_ctlun.ip6_un1.ip6_un1_hlim
95 All fields are in network-byte order.
96 Any options specified (see
98 below) must also be specified in network-byte order.
101 specifies the flow ID.
103 specifies the payload length.
105 specifies the type of the next header.
107 specifies the hop limit.
111 specify the class and the bottom 4 bits specify the version.
116 specify the source and destination addresses.
118 The IPv6 header may be followed by any number of extension headers that start
119 with the following generic definition:
120 .Bd -literal -offset indent
127 IPv6 allows header options on packets to manipulate the behavior of the
129 These options and other control requests are accessed with the
133 system calls at level
135 and by using ancillary data in
139 They can be used to access most of the fields in the IPv6 header and
142 The following socket options are supported:
144 .\" .It Dv IPV6_OPTIONS
145 .It Dv IPV6_UNICAST_HOPS Fa "int *"
146 Get or set the default hop limit header field for outgoing unicast
147 datagrams sent on this socket.
148 .\" .It Dv IPV6_RECVOPTS Fa "int *"
149 .\" Get or set the status of whether all header options will be
150 .\" delivered along with the datagram when it is received.
151 .\" .It Dv IPV6_RECVRETOPTS Fa "int *"
152 .\" Get or set the status of whether header options will be delivered
154 .\" .It Dv IPV6_RECVDSTADDR Fa "int *"
155 .\" Get or set the status of whether datagrams are received with
156 .\" destination addresses.
157 .\" .It Dv IPV6_RETOPTS
158 .\" Get or set IPv6 options.
159 .It Dv IPV6_MULTICAST_IF Fa "u_int *"
160 Get or set the interface from which multicast packets will be sent.
161 For hosts with multiple interfaces, each multicast transmission is sent
162 from the primary network interface.
163 The interface is specified as its index as provided by
164 .Xr if_nametoindex 3 .
165 A value of zero specifies the default interface.
166 .It Dv IPV6_MULTICAST_HOPS Fa "int *"
167 Get or set the default hop limit header field for outgoing multicast
168 datagrams sent on this socket.
169 This option controls the scope of multicast datagram transmissions.
171 Datagrams with a hop limit of 1 are not forwarded beyond the local
173 Multicast datagrams with a hop limit of zero will not be transmitted on
174 any network but may be delivered locally if the sending host belongs to
175 the destination group and if multicast loopback (see below) has not been
176 disabled on the sending socket.
177 Multicast datagrams with a hop limit greater than 1 may be forwarded to
178 the other networks if a multicast router (such as
179 .Xr mrouted 8 Pq Pa ports/net/mrouted )
180 is attached to the local network.
181 .It Dv IPV6_MULTICAST_LOOP Fa "u_int *"
182 Get or set the status of whether multicast datagrams will be looped back
183 for local delivery when a multicast datagram is sent to a group to which
184 the sending host belongs.
186 This option improves performance for applications that may have no more
187 than one instance on a single host (such as a router daemon) by
188 eliminating the overhead of receiving their own transmissions.
189 It should generally not be used by applications for which there may be
190 more than one instance on a single host (such as a conferencing program)
191 or for which the sender does not belong to the destination group
192 (such as a time-querying program).
194 A multicast datagram sent with an initial hop limit greater than 1 may
195 be delivered to the sending host on a different interface from that on
196 which it was sent if the host belongs to the destination group on that
198 The multicast loopback control option has no effect on such delivery.
199 .It Dv IPV6_JOIN_GROUP Fa "struct ipv6_mreq *"
200 Join a multicast group.
201 A host must become a member of a multicast group before it can receive
202 datagrams sent to the group.
205 struct in6_addr ipv6mr_multiaddr;
206 unsigned int ipv6mr_interface;
211 may be set to zeroes to choose the default multicast interface or to the
212 index of a particular multicast-capable interface if the host is
214 Membership is associated with a single interface; programs running on
215 multihomed hosts may need to join the same group on more than one
218 If the multicast address is unspecified (i.e., all zeroes), messages
219 from all multicast addresses will be accepted by this group.
220 Note that setting to this value requires superuser privileges.
221 .It Dv IPV6_LEAVE_GROUP Fa "struct ipv6_mreq *"
222 Drop membership from the associated multicast group.
223 Memberships are automatically dropped when the socket is closed or when
225 .It Dv IPV6_ORIGDSTADDR Fa "int *"
226 Get or set whether a datagram's original destination address and port are
227 returned as ancillary data along with the payload in subsequent
230 The information is stored in the ancillary data as a
233 .It Dv IPV6_PORTRANGE Fa "int *"
234 Get or set the allocation policy of ephemeral ports for when the kernel
235 automatically binds a local address to this socket.
236 The following values are available:
238 .Bl -tag -width IPV6_PORTRANGE_DEFAULT -compact
239 .It Dv IPV6_PORTRANGE_DEFAULT
240 Use the regular range of non-reserved ports (varies, see
242 .It Dv IPV6_PORTRANGE_HIGH
243 Use a high range (varies, see
245 .It Dv IPV6_PORTRANGE_LOW
246 Use a low, reserved range (600\-1023, see
249 .It Dv IPV6_PKTINFO Fa "int *"
250 Get or set whether additional information about subsequent packets will
251 be provided as ancillary data along with the payload in subsequent
254 The information is stored in the following structure in the ancillary
258 struct in6_addr ipi6_addr; /* src/dst IPv6 address */
259 unsigned int ipi6_ifindex; /* send/recv if index */
262 .It Dv IPV6_HOPLIMIT Fa "int *"
263 Get or set whether the hop limit header field from subsequent packets
264 will be provided as ancillary data along with the payload in subsequent
267 The value is stored as an
269 in the ancillary data returned.
270 .\" .It Dv IPV6_NEXTHOP Fa "int *"
271 .\" Get or set whether the address of the next hop for subsequent
272 .\" packets will be provided as ancillary data along with the payload in
276 .\" The option is stored as a
278 .\" structure in the ancillary data returned.
280 .\" This option requires superuser privileges.
281 .It Dv IPV6_HOPOPTS Fa "int *"
282 Get or set whether the hop-by-hop options from subsequent packets will be
283 provided as ancillary data along with the payload in subsequent
286 The option is stored in the following structure in the ancillary data
290 uint8_t ip6h_nxt; /* next header */
291 uint8_t ip6h_len; /* length in units of 8 octets */
292 /* followed by options */
298 routine and family of routines may be used to manipulate this data.
300 This option requires superuser privileges.
301 .It Dv IPV6_DSTOPTS Fa "int *"
302 Get or set whether the destination options from subsequent packets will
303 be provided as ancillary data along with the payload in subsequent
306 The option is stored in the following structure in the ancillary data
310 uint8_t ip6d_nxt; /* next header */
311 uint8_t ip6d_len; /* length in units of 8 octets */
312 /* followed by options */
318 routine and family of routines may be used to manipulate this data.
320 This option requires superuser privileges.
321 .It Dv IPV6_TCLASS Fa "int *"
322 Get or set the value of the traffic class field used for outgoing datagrams
324 The value must be between \-1 and 255.
325 A value of \-1 resets to the default value.
326 .It Dv IPV6_RECVTCLASS Fa "int *"
327 Get or set the status of whether the traffic class header field will be
328 provided as ancillary data along with the payload in subsequent
331 The header field is stored as a single value of type
333 .It Dv IPV6_RTHDR Fa "int *"
334 Get or set whether the routing header from subsequent packets will be
335 provided as ancillary data along with the payload in subsequent
338 The header is stored in the following structure in the ancillary data
342 uint8_t ip6r_nxt; /* next header */
343 uint8_t ip6r_len; /* length in units of 8 octets */
344 uint8_t ip6r_type; /* routing type */
345 uint8_t ip6r_segleft; /* segments left */
346 /* followed by routing-type-specific data */
352 routine and family of routines may be used to manipulate this data.
354 This option requires superuser privileges.
355 .It Dv IPV6_PKTOPTIONS Fa "struct cmsghdr *"
356 Get or set all header options and extension headers at one time on the
357 last packet sent or received on the socket.
358 All options must fit within the size of an mbuf (see
360 Options are specified as a series of
362 structures followed by corresponding values.
367 to one of the other values in this list, and trailing data to the option
369 When setting options, if the length
373 is zero, all header options will be reset to their default values.
374 Otherwise, the length should specify the size the series of control
379 to specify option values, the ancillary data used in these calls that
380 correspond to the desired header options may be directly specified as
381 the control message in the series of control messages provided as the
384 .It Dv IPV6_CHECKSUM Fa "int *"
385 Get or set the byte offset into a packet where the 16-bit checksum is
387 When set, this byte offset is where incoming packets will be expected
388 to have checksums of their data stored and where outgoing packets will
389 have checksums of their data computed and stored by the kernel.
390 A value of \-1 specifies that no checksums will be checked on incoming
391 packets and that no checksums will be computed or stored on outgoing
393 The offset of the checksum for ICMPv6 sockets cannot be relocated or
395 .It Dv IPV6_V6ONLY Fa "int *"
396 Get or set whether only IPv6 connections can be made to this socket.
397 For wildcard sockets, this can restrict connections to IPv6 only.
400 .\"IPv6 sockets are always IPv6-only, so the socket option is read-only
402 .It Dv IPV6_USE_MIN_MTU Fa "int *"
403 Get or set whether the minimal IPv6 maximum transmission unit (MTU) size
404 will be used to avoid fragmentation from occurring for subsequent
406 .It Dv IPV6_AUTH_LEVEL Fa "int *"
409 authentication level.
410 .It Dv IPV6_ESP_TRANS_LEVEL Fa "int *"
411 Get or set the ESP transport level.
412 .It Dv IPV6_ESP_NETWORK_LEVEL Fa "int *"
413 Get or set the ESP encapsulation level.
414 .It Dv IPV6_IPCOMP_LEVEL Fa "int *"
422 .\" .Dv IPV6_NEXTHOP ,
429 options will return ancillary data along with payload contents in subsequent
437 set to respective option name value (e.g.,
438 .Dv IPV6_HOPTLIMIT ) .
439 Some of these options may also be used directly as ancillary
443 to set options on the packet being transmitted by the call.
448 For these options, the ancillary data object value format is the same
449 as the value returned as explained for each when received with
454 to specify options on particular packets works only on UDP and raw sockets.
455 To manipulate header options for packets on TCP sockets, only the socket
458 In some cases, there are multiple APIs defined for manipulating an IPv6
460 A good example is the outgoing interface for multicast datagrams, which
462 .Dv IPV6_MULTICAST_IF
463 socket option, through the
465 option, and through the
467 field of the socket address passed to the
471 Resolving these conflicts is implementation dependent.
472 This implementation determines the value in the following way:
473 options specified by using ancillary data (i.e.,
475 are considered first,
476 options specified by using
480 options are considered second,
481 options specified by using the individual, basic, and direct socket
483 .Dv IPV6_UNICAST_HOPS )
484 are considered third,
485 and options specified in the socket address supplied to
489 IPv6 multicasting is supported only on
495 and only on networks where the interface driver supports
497 Socket options (see above) that manipulate membership of
498 multicast groups and other multicast options include
499 .Dv IPV6_MULTICAST_IF ,
500 .Dv IPV6_MULTICAST_HOPS ,
501 .Dv IPV6_MULTICAST_LOOP ,
502 .Dv IPV6_LEAVE_GROUP ,
504 .Dv IPV6_JOIN_GROUP .
506 Raw IPv6 sockets are connectionless and are normally used with the
512 call may be used to fix the destination address for future outgoing
515 may instead be used and the
517 call may be used to fix the source address for future outgoing
518 packets instead of having the kernel choose a source address.
524 raw socket input is constrained to only packets with their
525 source address matching the socket destination address if
527 was used and to packets with their destination address
528 matching the socket source address if
536 is zero, the default protocol
538 is used for outgoing packets.
539 For incoming packets, protocols recognized by kernel are
541 passed to the application socket (e.g.,
545 except for some ICMPv6 messages.
546 The ICMPv6 messages not passed to raw sockets include echo, timestamp,
547 and address mask requests.
550 is non-zero, only packets with this protocol will be passed to the
553 IPv6 fragments are also not passed to application sockets until
554 they have been reassembled.
555 If reception of all packets is desired, link-level access (such as
557 must be used instead.
559 Outgoing packets automatically have an IPv6 header prepended to them
560 (based on the destination address and the protocol number the socket
562 Incoming packets are received by an application without the IPv6 header
563 or any extension headers.
565 Outgoing packets will be fragmented automatically by the kernel if they
567 Incoming packets will be reassembled before being sent to the raw socket,
568 so packet fragments or fragment headers will never be seen on a raw socket.
570 The following determines the hop limit on the next packet received:
582 (void)memset(&m, 0, sizeof(m));
583 (void)memset(&iov, 0, sizeof(iov));
585 iov[0].iov_base = data; /* buffer for packet payload */
586 iov[0].iov_len = sizeof(data); /* expected packet length */
588 m.msg_name = &from; /* sockaddr_in6 of peer */
589 m.msg_namelen = sizeof(from);
592 m.msg_control = (caddr_t)buf; /* buffer for control messages */
593 m.msg_controllen = sizeof(buf);
596 * Enable the hop limit value from received packets to be
597 * returned along with the payload.
600 if (setsockopt(s, IPPROTO_IPV6, IPV6_HOPLIMIT, &optval,
601 sizeof(optval)) == -1)
602 err(1, "setsockopt");
606 if (recvmsg(s, &m, 0) == -1)
608 for (cm = CMSG_FIRSTHDR(&m); cm != NULL;
609 cm = CMSG_NXTHDR(&m, cm)) {
610 if (cm->cmsg_level == IPPROTO_IPV6 &&
611 cm->cmsg_type == IPV6_HOPLIMIT &&
612 cm->cmsg_len == CMSG_LEN(sizeof(int))) {
614 (void)printf("hop limit: %d\en",
615 *(int *)CMSG_DATA(cm));
622 A socket operation may fail with one of the following errors returned:
623 .Bl -tag -width EADDRNOTAVAILxx
625 when trying to establish a connection on a socket which
626 already has one or when trying to send a datagram with the destination
627 address specified and the socket is already connected.
629 when trying to send a datagram, but
630 no destination address is specified, and the socket has not been
633 when the system runs out of memory for
634 an internal data structure.
635 .It Bq Er EADDRNOTAVAIL
636 when an attempt is made to create a
637 socket with a network address for which no network interface
640 when an attempt is made to create
641 a raw IPv6 socket by a non-privileged process.
644 The following errors specific to IPv6 may occur when setting or getting
646 .Bl -tag -width EADDRNOTAVAILxx
648 An unknown socket option name was given.
650 An ancillary data object was improperly formed.
659 .Xr if_nametoindex 3 ,
660 .Xr inet6_opt_init 3 ,
671 .%T Advanced Sockets API for IPv6
678 .%T Internet Protocol, Version 6 (IPv6) Specification
687 .%T Basic Socket Interface Extensions for IPv6
697 .%T Basic Socket Interface Extensions for IPv6
706 .%T Advanced Sockets Application Program Interface (API) for IPv6
713 .%T Internet Protocol, Version 6 (IPv6) Specification
721 .%T UNIX Network Programming, 3rd Edition
722 .%I Addison-Wesley Professional
726 Most of the socket options are defined in RFC 2292 / 3542 or
730 socket option and the conflict resolution rule are not defined in the
731 RFCs and should be considered implementation dependent.