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1 .\" This man page is Copyright (C) 2000 Andi Kleen <ak@muc.de>.
2 .\"
3 .\" %%%LICENSE_START(VERBATIM_ONE_PARA)
4 .\" Permission is granted to distribute possibly modified copies
5 .\" of this page provided the header is included verbatim,
6 .\" and in case of nontrivial modification author and date
7 .\" of the modification is added to the header.
8 .\" %%%LICENSE_END
9 .\"
10 .\" $Id: ipv6.7,v 1.3 2000/12/20 18:10:31 ak Exp $
11 .\"
12 .\" The following socket options are undocumented
13 .\" All of the following are from:
14 .\" commit 333fad5364d6b457c8d837f7d05802d2aaf8a961
15 .\" Author: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
16 .\" Support several new sockopt / ancillary data in Advanced API (RFC3542).
17 .\" IPV6_2292PKTINFO (2.6.14)
18 .\" Formerly IPV6_PKTINFO
19 .\" IPV6_2292HOPOPTS (2.6.14)
20 .\" Formerly IPV6_HOPOPTS, which is documented
21 .\" IPV6_2292DSTOPTS (2.6.14)
22 .\" Formerly IPV6_DSTOPTS, which is documented
23 .\" IPV6_2292RTHDR (2.6.14)
24 .\" Formerly IPV6_RTHDR, which is documented
25 .\" IPV6_2292PKTOPTIONS (2.6.14)
26 .\" Formerly IPV6_PKTOPTIONS
27 .\" IPV6_2292HOPLIMIT (2.6.14)
28 .\" Formerly IPV6_HOPLIMIT, which is documented
29 .\"
30 .\" IPV6_RECVHOPLIMIT (2.6.14)
31 .\" IPV6_RECVHOPOPTS (2.6.14)
32 .\" IPV6_RTHDRDSTOPTS (2.6.14)
33 .\" IPV6_RECVRTHDR (2.6.14)
34 .\" IPV6_RECVDSTOPTS (2.6.14)
35 .\"
36 .\" IPV6_RECVPATHMTU (2.6.35, flag value added in 2.6.14)
37 .\" commit 793b14731686595a741d9f47726ad8b9a235385a
38 .\" Author: Brian Haley <brian.haley@hp.com>
39 .\" IPV6_PATHMTU (2.6.35, flag value added in 2.6.14)
40 .\" commit 793b14731686595a741d9f47726ad8b9a235385a
41 .\" Author: Brian Haley <brian.haley@hp.com>
42 .\" IPV6_DONTFRAG (2.6.35, flag value added in 2.6.14)
43 .\" commit 793b14731686595a741d9f47726ad8b9a235385a
44 .\" Author: Brian Haley <brian.haley@hp.com>
45 .\" commit 4b340ae20d0e2366792abe70f46629e576adaf5e
46 .\" Author: Brian Haley <brian.haley@hp.com>
47 .\"
48 .\" IPV6_RECVTCLASS (2.6.14)
49 .\" commit 41a1f8ea4fbfcdc4232f023732584aae2220de31
50 .\" Author: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
51 .\" Based on patch from David L Stevens <dlstevens@us.ibm.com>
52 .\"
53 .\" IPV6_CHECKSUM (2.2)
54 .\" IPV6_NEXTHOP (2.2)
55 .\" IPV6_JOIN_ANYCAST (2.4.21 / 2.6)
56 .\" IPV6_LEAVE_ANYCAST (2.4.21 / 2.6)
57 .\" IPV6_FLOWLABEL_MGR (2.2.7 / 2.4)
58 .\" IPV6_FLOWINFO_SEND (2.2.7 / 2.4)
59 .\" IPV6_IPSEC_POLICY (2.6)
60 .\" IPV6_XFRM_POLICY (2.6)
61 .\" IPV6_TCLASS (2.6)
62 .\"
63 .\" IPV6_ADDR_PREFERENCES (2.6.26)
64 .\" commit 7cbca67c073263c179f605bdbbdc565ab29d801d
65 .\" Author: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
66 .\" IPV6_MINHOPCOUNT (2.6.35)
67 .\" commit e802af9cabb011f09b9c19a82faef3dd315f27eb
68 .\" Author: Stephen Hemminger <shemminger@vyatta.com>
69 .\" IPV6_ORIGDSTADDR (2.6.37)
70 .\" Actually a CMSG rather than a sockopt?
71 .\" In header file, we have IPV6_RECVORIGDSTADDR == IPV6_ORIGDSTADDR
72 .\" commit 6c46862280c5f55eda7750391bc65cd7e08c7535
73 .\" Author: Balazs Scheidler <bazsi@balabit.hu>
74 .\" IPV6_RECVORIGDSTADDR (2.6.37)
75 .\" commit 6c46862280c5f55eda7750391bc65cd7e08c7535
76 .\" Author: Balazs Scheidler <bazsi@balabit.hu>
77 .\" Support for IPV6_RECVORIGDSTADDR sockopt for UDP sockets
78 .\" were contributed by Harry Mason.
79 .\" IPV6_TRANSPARENT (2.6.37)
80 .\" commit 6c46862280c5f55eda7750391bc65cd7e08c7535
81 .\" Author: Balazs Scheidler <bazsi@balabit.hu>
82 .\" IPV6_UNICAST_IF (3.4)
83 .\" commit c4062dfc425e94290ac427a98d6b4721dd2bc91f
84 .\" Author: Erich E. Hoover <ehoover@mines.edu>
85 .\"
86 .TH IPV6 7 2021-03-22 "Linux" "Linux Programmer's Manual"
87 .SH NAME
88 ipv6 \- Linux IPv6 protocol implementation
89 .SH SYNOPSIS
90 .nf
91 .B #include <sys/socket.h>
92 .B #include <netinet/in.h>
93 .PP
94 .IB tcp6_socket " = socket(AF_INET6, SOCK_STREAM, 0);"
95 .IB raw6_socket " = socket(AF_INET6, SOCK_RAW, " protocol ");"
96 .IB udp6_socket " = socket(AF_INET6, SOCK_DGRAM, " protocol ");"
97 .fi
98 .SH DESCRIPTION
99 Linux 2.2 optionally implements the Internet Protocol, version 6.
100 This man page contains a description of the IPv6 basic API as
101 implemented by the Linux kernel and glibc 2.1.
102 The interface
103 is based on the BSD sockets interface; see
104 .BR socket (7).
105 .PP
106 The IPv6 API aims to be mostly compatible with the
107 IPv4 API (see
108 .BR ip (7)).
109 Only differences are described in this man page.
110 .PP
111 To bind an
112 .B AF_INET6
113 socket to any process, the local address should be copied from the
114 .I in6addr_any
115 variable which has
116 .I in6_addr
117 type.
118 In static initializations,
119 .B IN6ADDR_ANY_INIT
120 may also be used, which expands to a constant expression.
121 Both of them are in network byte order.
122 .PP
123 The IPv6 loopback address (::1) is available in the global
124 .I in6addr_loopback
125 variable.
126 For initializations,
127 .B IN6ADDR_LOOPBACK_INIT
128 should be used.
129 .PP
130 IPv4 connections can be handled with the v6 API by using the
131 v4-mapped-on-v6 address type;
132 thus a program needs to support only this API type to
133 support both protocols.
134 This is handled transparently by the address
135 handling functions in the C library.
136 .PP
137 IPv4 and IPv6 share the local port space.
138 When you get an IPv4 connection
139 or packet to an IPv6 socket, its source address will be mapped
140 to v6 and it will be mapped to v6.
141 .SS Address format
142 .in +4n
143 .EX
144 struct sockaddr_in6 {
145 sa_family_t sin6_family; /* AF_INET6 */
146 in_port_t sin6_port; /* port number */
147 uint32_t sin6_flowinfo; /* IPv6 flow information */
148 struct in6_addr sin6_addr; /* IPv6 address */
149 uint32_t sin6_scope_id; /* Scope ID (new in 2.4) */
150 };
152 struct in6_addr {
153 unsigned char s6_addr[16]; /* IPv6 address */
154 };
155 .EE
156 .in
157 .PP
158 .I sin6_family
159 is always set to
160 .BR AF_INET6 ;
161 .I sin6_port
162 is the protocol port (see
163 .I sin_port
164 in
165 .BR ip (7));
166 .I sin6_flowinfo
167 is the IPv6 flow identifier;
168 .I sin6_addr
169 is the 128-bit IPv6 address.
170 .I sin6_scope_id
171 is an ID depending on the scope of the address.
172 It is new in Linux 2.4.
173 Linux supports it only for link-local addresses, in that case
174 .I sin6_scope_id
175 contains the interface index (see
176 .BR netdevice (7))
177 .PP
178 IPv6 supports several address types: unicast to address a single
179 host, multicast to address a group of hosts,
180 anycast to address the nearest member of a group of hosts
181 (not implemented in Linux), IPv4-on-IPv6 to
182 address an IPv4 host, and other reserved address types.
183 .PP
184 The address notation for IPv6 is a group of 8 4-digit hexadecimal
185 numbers, separated with a \(aq:\(aq.
186 \&"::" stands for a string of 0 bits.
187 Special addresses are ::1 for loopback and ::FFFF:<IPv4 address>
188 for IPv4-mapped-on-IPv6.
189 .PP
190 The port space of IPv6 is shared with IPv4.
191 .SS Socket options
192 IPv6 supports some protocol-specific socket options that can be set with
193 .BR setsockopt (2)
194 and read with
195 .BR getsockopt (2).
196 The socket option level for IPv6 is
197 .BR IPPROTO_IPV6 .
198 A boolean integer flag is zero when it is false, otherwise true.
199 .TP
200 .B IPV6_ADDRFORM
201 Turn an
202 .B AF_INET6
203 socket into a socket of a different address family.
204 Only
205 .B AF_INET
206 is currently supported for that.
207 It is allowed only for IPv6 sockets
208 that are connected and bound to a v4-mapped-on-v6 address.
209 The argument is a pointer to an integer containing
210 .BR AF_INET .
211 This is useful to pass v4-mapped sockets as file descriptors to
212 programs that don't know how to deal with the IPv6 API.
213 .TP
214 .B IPV6_ADD_MEMBERSHIP, IPV6_DROP_MEMBERSHIP
215 Control membership in multicast groups.
216 Argument is a pointer to a
217 .IR "struct ipv6_mreq" .
218 .TP
219 .B IPV6_MTU
220 .BR getsockopt ():
221 Retrieve the current known path MTU of the current socket.
222 Valid only when the socket has been connected.
223 Returns an integer.
224 .IP
225 .BR setsockopt ():
226 Set the MTU to be used for the socket.
227 The MTU is limited by the device
228 MTU or the path MTU when path MTU discovery is enabled.
229 Argument is a pointer to integer.
230 .TP
231 .B IPV6_MTU_DISCOVER
232 Control path-MTU discovery on the socket.
233 See
234 .B IP_MTU_DISCOVER
235 in
236 .BR ip (7)
237 for details.
238 .TP
239 .B IPV6_MULTICAST_HOPS
240 Set the multicast hop limit for the socket.
241 Argument is a pointer to an
242 integer.
243 \-1 in the value means use the route default, otherwise it should be
244 between 0 and 255.
245 .TP
246 .B IPV6_MULTICAST_IF
247 Set the device for outgoing multicast packets on the socket.
248 This is allowed only for
249 .B SOCK_DGRAM
250 and
251 .B SOCK_RAW
252 socket.
253 The argument is a pointer to an interface index (see
254 .BR netdevice (7))
255 in an integer.
256 .TP
257 .B IPV6_MULTICAST_LOOP
258 Control whether the socket sees multicast packets that it has send itself.
259 Argument is a pointer to boolean.
260 .TP
261 .BR IPV6_RECVPKTINFO " (since Linux 2.6.14)"
262 Set delivery of the
263 .B IPV6_PKTINFO
264 control message on incoming datagrams.
265 Such control messages contain a
266 .IR "struct in6_pktinfo" ,
267 as per RFC 3542.
268 Allowed only for
269 .B SOCK_DGRAM
270 or
271 .B SOCK_RAW
272 sockets.
273 Argument is a pointer to a boolean value in an integer.
274 .TP
275 .nh
276 .B IPV6_RTHDR, IPV6_AUTHHDR, IPV6_DSTOPTS, IPV6_HOPOPTS, IPV6_FLOWINFO, IPV6_HOPLIMIT
277 .hy
278 Set delivery of control messages for incoming datagrams containing
279 extension headers from the received packet.
280 .B IPV6_RTHDR
281 delivers the routing header,
282 .B IPV6_AUTHHDR
283 delivers the authentication header,
284 .B IPV6_DSTOPTS
285 delivers the destination options,
286 .B IPV6_HOPOPTS
287 delivers the hop options,
288 .B IPV6_FLOWINFO
289 delivers an integer containing the flow ID,
290 .B IPV6_HOPLIMIT
291 delivers an integer containing the hop count of the packet.
292 The control messages have the same type as the socket option.
293 All these header options can also be set for outgoing packets
294 by putting the appropriate control message into the control buffer of
295 .BR sendmsg (2).
296 Allowed only for
297 .B SOCK_DGRAM
298 or
299 .B SOCK_RAW
300 sockets.
301 Argument is a pointer to a boolean value.
302 .TP
303 .B IPV6_RECVERR
304 Control receiving of asynchronous error options.
305 See
306 .B IP_RECVERR
307 in
308 .BR ip (7)
309 for details.
310 Argument is a pointer to boolean.
311 .TP
312 .B IPV6_ROUTER_ALERT
313 Pass forwarded packets containing a router alert hop-by-hop option to
314 this socket.
315 Allowed only for
316 .B SOCK_RAW
317 sockets.
318 The tapped packets are not forwarded by the kernel, it is the
319 user's responsibility to send them out again.
320 Argument is a pointer to an integer.
321 A positive integer indicates a router alert option value to intercept.
322 Packets carrying a router alert option with a value field containing
323 this integer will be delivered to the socket.
324 A negative integer disables delivery of packets with router alert options
325 to this socket.
326 .TP
327 .B IPV6_UNICAST_HOPS
328 Set the unicast hop limit for the socket.
329 Argument is a pointer to an integer.
330 \-1 in the value means use the route default,
331 otherwise it should be between 0 and 255.
332 .TP
333 .BR IPV6_V6ONLY " (since Linux 2.4.21 and 2.6)"
334 .\" See RFC 3493
335 If this flag is set to true (nonzero), then the socket is restricted
336 to sending and receiving IPv6 packets only.
337 In this case, an IPv4 and an IPv6 application can bind
338 to a single port at the same time.
339 .IP
340 If this flag is set to false (zero),
341 then the socket can be used to send and receive packets
342 to and from an IPv6 address or an IPv4-mapped IPv6 address.
343 .IP
344 The argument is a pointer to a boolean value in an integer.
345 .IP
346 The default value for this flag is defined by the contents of the file
347 .IR /proc/sys/net/ipv6/bindv6only .
348 The default value for that file is 0 (false).
349 .\" FLOWLABEL_MGR, FLOWINFO_SEND
350 .SH ERRORS
351 .TP
352 .B ENODEV
353 The user tried to
354 .BR bind (2)
355 to a link-local IPv6 address, but the
356 .I sin6_scope_id
357 in the supplied
358 .I sockaddr_in6
359 structure is not a valid
360 interface index.
361 .SH VERSIONS
362 Linux 2.4 will break binary compatibility for the
363 .I sockaddr_in6
364 for 64-bit
365 hosts by changing the alignment of
366 .I in6_addr
367 and adding an additional
368 .I sin6_scope_id
369 field.
370 The kernel interfaces stay compatible, but a program including
371 .I sockaddr_in6
372 or
373 .I in6_addr
374 into other structures may not be.
375 This is not
376 a problem for 32-bit hosts like i386.
377 .PP
378 The
379 .I sin6_flowinfo
380 field is new in Linux 2.4.
381 It is transparently passed/read by the kernel
382 when the passed address length contains it.
383 Some programs that pass a longer address buffer and then
384 check the outgoing address length may break.
385 .SH NOTES
386 The
387 .I sockaddr_in6
388 structure is bigger than the generic
389 .IR sockaddr .
390 Programs that assume that all address types can be stored safely in a
391 .I struct sockaddr
392 need to be changed to use
393 .I struct sockaddr_storage
394 for that instead.
395 .PP
396 .BR SOL_IP ,
397 .BR SOL_IPV6 ,
398 .BR SOL_ICMPV6 ,
399 and other
400 .B SOL_*
401 socket options are nonportable variants of
402 .BR IPPROTO_* .
403 See also
404 .BR ip (7).
405 .SH BUGS
406 The IPv6 extended API as in RFC\ 2292 is currently only partly
407 implemented;
408 although the 2.2 kernel has near complete support for receiving options,
409 the macros for generating IPv6 options are missing in glibc 2.1.
410 .PP
411 IPSec support for EH and AH headers is missing.
412 .PP
413 Flow label management is not complete and not documented here.
414 .PP
415 This man page is not complete.
416 .SH SEE ALSO
417 .BR cmsg (3),
418 .BR ip (7)
419 .PP
420 RFC\ 2553: IPv6 BASIC API;
421 Linux tries to be compliant to this.
422 RFC\ 2460: IPv6 specification.