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 uint32_t ip6_un1_flow; /* 20 bits of flow ID */
79 uint16_t ip6_un1_plen; /* payload length */
80 uint8_t ip6_un1_nxt; /* next header */
81 uint8_t ip6_un1_hlim; /* hop limit */
83 uint8_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_ORIGDSTADDR Fa "int *"
228 Get or set whether a datagram's original destination address and port are
229 returned as ancillary data along with the payload in subsequent
232 The information is stored in the ancillary data as a
235 .It Dv IPV6_PORTRANGE Fa "int *"
236 Get or set the allocation policy of ephemeral ports for when the kernel
237 automatically binds a local address to this socket.
238 The following values are available:
240 .Bl -tag -width IPV6_PORTRANGE_DEFAULT -compact
241 .It Dv IPV6_PORTRANGE_DEFAULT
242 Use the regular range of non-reserved ports (varies, see
244 .It Dv IPV6_PORTRANGE_HIGH
245 Use a high range (varies, see
247 .It Dv IPV6_PORTRANGE_LOW
248 Use a low, reserved range (600\-1023, see
251 .It Dv IPV6_PKTINFO Fa "int *"
252 Get or set whether additional information about subsequent packets will
253 be provided as ancillary data along with the payload in subsequent
256 The information is stored in the following structure in the ancillary
260 struct in6_addr ipi6_addr; /* src/dst IPv6 address */
261 unsigned int ipi6_ifindex; /* send/recv if index */
264 .It Dv IPV6_HOPLIMIT Fa "int *"
265 Get or set whether the hop limit header field from subsequent packets
266 will be provided as ancillary data along with the payload in subsequent
269 The value is stored as an
271 in the ancillary data returned.
272 .\" .It Dv IPV6_NEXTHOP Fa "int *"
273 .\" Get or set whether the address of the next hop for subsequent
274 .\" packets will be provided as ancillary data along with the payload in
278 .\" The option is stored as a
280 .\" structure in the ancillary data returned.
282 .\" This option requires superuser privileges.
283 .It Dv IPV6_HOPOPTS Fa "int *"
284 Get or set whether the hop-by-hop options from subsequent packets will be
285 provided as ancillary data along with the payload in subsequent
288 The option is stored in the following structure in the ancillary data
292 uint8_t ip6h_nxt; /* next header */
293 uint8_t ip6h_len; /* length in units of 8 octets */
294 /* followed by options */
300 routine and family of routines may be used to manipulate this data.
302 This option requires superuser privileges.
303 .It Dv IPV6_DSTOPTS Fa "int *"
304 Get or set whether the destination options from subsequent packets will
305 be provided as ancillary data along with the payload in subsequent
308 The option is stored in the following structure in the ancillary data
312 uint8_t ip6d_nxt; /* next header */
313 uint8_t ip6d_len; /* length in units of 8 octets */
314 /* followed by options */
320 routine and family of routines may be used to manipulate this data.
322 This option requires superuser privileges.
323 .It Dv IPV6_TCLASS Fa "int *"
324 Get or set the value of the traffic class field used for outgoing datagrams
326 The value must be between \-1 and 255.
327 A value of \-1 resets to the default value.
328 .It Dv IPV6_RECVTCLASS Fa "int *"
329 Get or set the status of whether the traffic class header field will be
330 provided as ancillary data along with the payload in subsequent
333 The header field is stored as a single value of type
335 .It Dv IPV6_RTHDR Fa "int *"
336 Get or set whether the routing header from subsequent packets will be
337 provided as ancillary data along with the payload in subsequent
340 The header is stored in the following structure in the ancillary data
344 uint8_t ip6r_nxt; /* next header */
345 uint8_t ip6r_len; /* length in units of 8 octets */
346 uint8_t ip6r_type; /* routing type */
347 uint8_t ip6r_segleft; /* segments left */
348 /* followed by routing-type-specific data */
354 routine and family of routines may be used to manipulate this data.
356 This option requires superuser privileges.
357 .It Dv IPV6_PKTOPTIONS Fa "struct cmsghdr *"
358 Get or set all header options and extension headers at one time on the
359 last packet sent or received on the socket.
360 All options must fit within the size of an mbuf (see
362 Options are specified as a series of
364 structures followed by corresponding values.
369 to one of the other values in this list, and trailing data to the option
371 When setting options, if the length
375 is zero, all header options will be reset to their default values.
376 Otherwise, the length should specify the size the series of control
381 to specify option values, the ancillary data used in these calls that
382 correspond to the desired header options may be directly specified as
383 the control message in the series of control messages provided as the
386 .It Dv IPV6_CHECKSUM Fa "int *"
387 Get or set the byte offset into a packet where the 16-bit checksum is
389 When set, this byte offset is where incoming packets will be expected
390 to have checksums of their data stored and where outgoing packets will
391 have checksums of their data computed and stored by the kernel.
392 A value of \-1 specifies that no checksums will be checked on incoming
393 packets and that no checksums will be computed or stored on outgoing
395 The offset of the checksum for ICMPv6 sockets cannot be relocated or
397 .It Dv IPV6_V6ONLY Fa "int *"
398 Get or set whether only IPv6 connections can be made to this socket.
399 For wildcard sockets, this can restrict connections to IPv6 only.
402 .\"IPv6 sockets are always IPv6-only, so the socket option is read-only
404 .It Dv IPV6_USE_MIN_MTU Fa "int *"
405 Get or set whether the minimal IPv6 maximum transmission unit (MTU) size
406 will be used to avoid fragmentation from occurring for subsequent
408 .It Dv IPV6_AUTH_LEVEL Fa "int *"
411 authentication level.
412 .It Dv IPV6_ESP_TRANS_LEVEL Fa "int *"
413 Get or set the ESP transport level.
414 .It Dv IPV6_ESP_NETWORK_LEVEL Fa "int *"
415 Get or set the ESP encapsulation level.
416 .It Dv IPV6_IPCOMP_LEVEL Fa "int *"
424 .\" .Dv IPV6_NEXTHOP ,
431 options will return ancillary data along with payload contents in subsequent
439 set to respective option name value (e.g.,
440 .Dv IPV6_HOPTLIMIT ) .
441 Some of these options may also be used directly as ancillary
445 to set options on the packet being transmitted by the call.
450 For these options, the ancillary data object value format is the same
451 as the value returned as explained for each when received with
456 to specify options on particular packets works only on UDP and raw sockets.
457 To manipulate header options for packets on TCP sockets, only the socket
460 In some cases, there are multiple APIs defined for manipulating an IPv6
462 A good example is the outgoing interface for multicast datagrams, which
464 .Dv IPV6_MULTICAST_IF
465 socket option, through the
467 option, and through the
469 field of the socket address passed to the
473 Resolving these conflicts is implementation dependent.
474 This implementation determines the value in the following way:
475 options specified by using ancillary data (i.e.,
477 are considered first,
478 options specified by using
482 options are considered second,
483 options specified by using the individual, basic, and direct socket
485 .Dv IPV6_UNICAST_HOPS )
486 are considered third,
487 and options specified in the socket address supplied to
491 IPv6 multicasting is supported only on
497 and only on networks where the interface driver supports
499 Socket options (see above) that manipulate membership of
500 multicast groups and other multicast options include
501 .Dv IPV6_MULTICAST_IF ,
502 .Dv IPV6_MULTICAST_HOPS ,
503 .Dv IPV6_MULTICAST_LOOP ,
504 .Dv IPV6_LEAVE_GROUP ,
506 .Dv IPV6_JOIN_GROUP .
508 Raw IPv6 sockets are connectionless and are normally used with the
514 call may be used to fix the destination address for future outgoing
517 may instead be used and the
519 call may be used to fix the source address for future outgoing
520 packets instead of having the kernel choose a source address.
526 raw socket input is constrained to only packets with their
527 source address matching the socket destination address if
529 was used and to packets with their destination address
530 matching the socket source address if
538 is zero, the default protocol
540 is used for outgoing packets.
541 For incoming packets, protocols recognized by kernel are
543 passed to the application socket (e.g.,
547 except for some ICMPv6 messages.
548 The ICMPv6 messages not passed to raw sockets include echo, timestamp,
549 and address mask requests.
552 is non-zero, only packets with this protocol will be passed to the
555 IPv6 fragments are also not passed to application sockets until
556 they have been reassembled.
557 If reception of all packets is desired, link-level access (such as
559 must be used instead.
561 Outgoing packets automatically have an IPv6 header prepended to them
562 (based on the destination address and the protocol number the socket
564 Incoming packets are received by an application without the IPv6 header
565 or any extension headers.
567 Outgoing packets will be fragmented automatically by the kernel if they
569 Incoming packets will be reassembled before being sent to the raw socket,
570 so packet fragments or fragment headers will never be seen on a raw socket.
572 The following determines the hop limit on the next packet received:
584 (void)memset(&m, 0, sizeof(m));
585 (void)memset(&iov, 0, sizeof(iov));
587 iov[0].iov_base = data; /* buffer for packet payload */
588 iov[0].iov_len = sizeof(data); /* expected packet length */
590 m.msg_name = &from; /* sockaddr_in6 of peer */
591 m.msg_namelen = sizeof(from);
594 m.msg_control = (caddr_t)buf; /* buffer for control messages */
595 m.msg_controllen = sizeof(buf);
598 * Enable the hop limit value from received packets to be
599 * returned along with the payload.
602 if (setsockopt(s, IPPROTO_IPV6, IPV6_HOPLIMIT, &optval,
603 sizeof(optval)) == -1)
604 err(1, "setsockopt");
608 if (recvmsg(s, &m, 0) == -1)
610 for (cm = CMSG_FIRSTHDR(&m); cm != NULL;
611 cm = CMSG_NXTHDR(&m, cm)) {
612 if (cm->cmsg_level == IPPROTO_IPV6 &&
613 cm->cmsg_type == IPV6_HOPLIMIT &&
614 cm->cmsg_len == CMSG_LEN(sizeof(int))) {
616 (void)printf("hop limit: %d\en",
617 *(int *)CMSG_DATA(cm));
624 A socket operation may fail with one of the following errors returned:
625 .Bl -tag -width EADDRNOTAVAILxx
627 when trying to establish a connection on a socket which
628 already has one or when trying to send a datagram with the destination
629 address specified and the socket is already connected.
631 when trying to send a datagram, but
632 no destination address is specified, and the socket has not been
635 when the system runs out of memory for
636 an internal data structure.
637 .It Bq Er EADDRNOTAVAIL
638 when an attempt is made to create a
639 socket with a network address for which no network interface
642 when an attempt is made to create
643 a raw IPv6 socket by a non-privileged process.
646 The following errors specific to IPv6 may occur when setting or getting
648 .Bl -tag -width EADDRNOTAVAILxx
650 An unknown socket option name was given.
652 An ancillary data object was improperly formed.
661 .Xr if_nametoindex 3 ,
662 .Xr inet6_opt_init 3 ,
673 .%T Advanced Sockets API for IPv6
680 .%T Internet Protocol, Version 6 (IPv6) Specification
689 .%T Basic Socket Interface Extensions for IPv6
699 .%T Basic Socket Interface Extensions for IPv6
708 .%T Advanced Sockets Application Program Interface (API) for IPv6
715 .%T Internet Protocol, Version 6 (IPv6) Specification
723 .%T UNIX Network Programming, 3rd Edition
724 .%I Addison-Wesley Professional
728 Most of the socket options are defined in RFC 2292 / 3542 or
732 socket option and the conflict resolution rule are not defined in the
733 RFCs and should be considered implementation dependent.