1IPV6(7) Linux Programmer's Manual IPV6(7)
2
6 ipv6, AF_INET6 - Linux IPv6 protocol implementation
7
9 #include <sys/socket.h>
10 #include <netinet/in.h>
11 tcp6_socket = socket(AF_INET6, SOCK_STREAM, 0);
13 raw6_socket = socket(AF_INET6, SOCK_RAW, protocol);
14 udp6_socket = socket(AF_INET6, SOCK_DGRAM, protocol);
15
17 Linux 2.2 optionally implements the Internet Protocol, version 6. This
18 man page contains a description of the IPv6 basic API as implemented by
19 the Linux kernel and glibc 2.1. The interface is based on the BSD
20 sockets interface; see socket(7).
21 The IPv6 API aims to be mostly compatible with the IPv4 API (see
23 ip(7)). Only differences are described in this man page.
24 To bind an AF_INET6 socket to any process, the local address should be
26 copied from the in6addr_any variable which has in6_addr type. In
27 static initializations, IN6ADDR_ANY_INIT may also be used, which
28 expands to a constant expression. Both of them are in network byte
29 order.
30 The IPv6 loopback address (::1) is available in the global
32 in6addr_loopback variable. For initializations, IN6ADDR_LOOPBACK_INIT
33 should be used.
34 IPv4 connections can be handled with the v6 API by using the v4-mapped-
36 on-v6 address type; thus a program only needs to support this API type
37 to support both protocols. This is handled transparently by the
38 address handling functions in the C library.
39 IPv4 and IPv6 share the local port space. When you get an IPv4 connec‐
41 tion or packet to a IPv6 socket, its source address will be mapped to
42 v6 and it will be mapped to v6.
43 Address Format
45 struct sockaddr_in6 {
46 sa_family_t sin6_family; /* AF_INET6 */
47 in_port_t sin6_port; /* port number */
48 uint32_t sin6_flowinfo; /* IPv6 flow information */
49 struct in6_addr sin6_addr; /* IPv6 address */
50 uint32_t sin6_scope_id; /* Scope ID (new in 2.4) */
51 };
52 struct in6_addr {
54 unsigned char s6_addr[16]; /* IPv6 address */
55 };
56 sin6_family is always set to AF_INET6; sin6_port is the protocol port
58 (see sin_port in ip(7)); sin6_flowinfo is the IPv6 flow identifier;
59 sin6_addr is the 128-bit IPv6 address. sin6_scope_id is an ID depend‐
60 ing on the scope of the address. It is new in Linux 2.4. Linux only
61 supports it for link scope addresses, in that case sin6_scope_id con‐
62 tains the interface index (see netdevice(7))
63 IPv6 supports several address types: unicast to address a single host,
65 multicast to address a group of hosts, anycast to address the nearest
66 member of a group of hosts (not implemented in Linux), IPv4-on-IPv6 to
67 address a IPv4 host, and other reserved address types.
68 The address notation for IPv6 is a group of 16 2-digit hexadecimal num‐
70 bers, separated with a ':'. "::" stands for a string of 0 bits. Spe‐
71 cial addresses are ::1 for loopback and ::FFFF:<IPv4 address> for
72 IPv4-mapped-on-IPv6.
73 The port space of IPv6 is shared with IPv4.
75 Socket Options
77 IPv6 supports some protocol-specific socket options that can be set
78 with setsockopt(2) and read with getsockopt(2). The socket option
79 level for IPv6 is IPPROTO_IPV6. A boolean integer flag is zero when it
80 is false, otherwise true.
81 IPV6_ADDRFORM
83 Turn an AF_INET6 socket into a socket of a different address
84 family. Only AF_INET is currently supported for that. It is
85 only allowed for IPv6 sockets that are connected and bound to a
86 v4-mapped-on-v6 address. The argument is a pointer to an inte‐
87 ger containing AF_INET. This is useful to pass v4-mapped sock‐
88 ets as file descriptors to programs that don't know how to deal
89 with the IPv6 API.
90 IPV6_ADD_MEMBERSHIP, IPV6_DROP_MEMBERSHIP
92 Control membership in multicast groups. Argument is a pointer
93 to a struct ipv6_mreq structure.
94 IPV6_MTU
96 Set the MTU to be used for the socket. The MTU is limited by
97 the device MTU or the path mtu when path mtu discovery is
98 enabled. Argument is a pointer to integer.
99 IPV6_MTU_DISCOVER
101 Control path mtu discovery on the socket. See IP_MTU_DISCOVER
102 in ip(7) for details.
103 IPV6_MULTICAST_HOPS
105 Set the multicast hop limit for the socket. Argument is a
106 pointer to an integer. -1 in the value means use the route
107 default, otherwise it should be between 0 and 255.
108 IPV6_MULTICAST_IF
110 Set the device for outgoing multicast packets on the socket.
111 This is only allowed for SOCK_DGRAM and SOCK_RAW socket. The
112 argument is a pointer to an interface index (see netdevice(7))
113 in an integer.
114 IPV6_MULTICAST_LOOP
116 Control whether the socket sees multicast packets that it has
117 send itself. Argument is a pointer to boolean.
118 IPV6_PKTINFO
120 Set delivery of the IPV6_PKTINFO control message on incoming
121 datagrams. Only allowed for SOCK_DGRAM or SOCK_RAW sockets.
122 Argument is a pointer to a boolean value in an integer.
123 IPV6_RTHDR, IPV6_AUTHHDR, IPV6_DSTOPS, IPV6_HOPOPTS, IPV6_FLOWINFO,
125 IPV6_HOPLIMIT
126 Set delivery of control messages for incoming datagrams contain‐
127 ing extension headers from the received packet. IPV6_RTHDR de‐
128 livers the routing header, IPV6_AUTHHDR delivers the authentica‐
129 tion header, IPV6_DSTOPTS delivers the destination options,
130 IPV6_HOPOPTS delivers the hop options, IPV6_FLOWINFO delivers an
131 integer containing the flow ID, IPV6_HOPLIMIT delivers an inte‐
132 ger containing the hop count of the packet. The control mes‐
133 sages have the same type as the socket option. All these header
134 options can also be set for outgoing packets by putting the ap‐
135 propriate control message into the control buffer of sendmsg(2).
136 Only allowed for SOCK_DGRAM or SOCK_RAW sockets. Argument is a
137 pointer to a boolean value.
138 IPV6_RECVERR
140 Control receiving of asynchronous error options. See IP_RECVERR
141 in ip(7) for details. Argument is a pointer to boolean.
142 IPV6_ROUTER_ALERT
144 Pass forwarded packets containing a router alert hop-by-hop op‐
145 tion to this socket. Only allowed for SOCK_RAW sockets. The
146 tapped packets are not forwarded by the kernel, it is the user's
147 responsibility to send them out again. Argument is a pointer to
148 an integer. A positive integer indicates a router alert option
149 value to intercept. Packets carrying a router alert option with
150 a value field containing this integer will be delivered to the
151 socket. A negative integer disables delivery of packets with
152 router alert options to this socket.
153 IPV6_UNICAST_HOPS
155 Set the unicast hop limit for the socket. Argument is a pointer
156 to an integer. -1 in the value means use the route default,
157 otherwise it should be between 0 and 255.
158 IPV6_V6ONLY (since Linux 2.4.21 and 2.6)
160 If this flag is set to true (nonzero), then the socket is re‐
161 stricted to sending and receiving IPv6 packets only. In this
162 case, an IPv4 and an IPv6 application can bind to a single port
163 at the same time.
164 If this flag is set to false (zero), then the socket can be used
166 to send and receive packets to and from an IPv6 address or an
167 IPv4-mapped IPv6 address.
168 The argument is a pointer to a boolean value in an integer.
170 The default value for this flag is defined by the contents of
172 the file /proc/sys/net/ipv6/bindv6only. The default value for
173 that file is 0 (false).
174
176 The older libinet6 libc5 based IPv6 API implementation for Linux is not
177 described here and may vary in details.
178 Linux 2.4 will break binary compatibility for the sockaddr_in6 for
180 64-bit hosts by changing the alignment of in6_addr and adding an addi‐
181 tional sin6_scope_id field. The kernel interfaces stay compatible, but
182 a program including sockaddr_in6 or in6_addr into other structures may
183 not be. This is not a problem for 32-bit hosts like i386.
184 The sin6_flowinfo field is new in Linux 2.4. It is transparently
186 passed/read by the kernel when the passed address length contains it.
187 Some programs that pass a longer address buffer and then check the out‐
188 going address length may break.
189
191 The sockaddr_in6 structure is bigger than the generic sockaddr. Pro‐
192 grams that assume that all address types can be stored safely in a
193 struct sockaddr need to be changed to use struct sockaddr_storage for
194 that instead.
195
197 The IPv6 extended API as in RFC 2292 is currently only partly imple‐
198 mented; although the 2.2 kernel has near complete support for receiving
199 options, the macros for generating IPv6 options are missing in glibc
200 2.1.
201 IPSec support for EH and AH headers is missing.
203 Flow label management is not complete and not documented here.
205 This man page is not complete.
207
209 cmsg(3), ip(7)
210 RFC 2553: IPv6 BASIC API. Linux tries to be compliant to this.
212 RFC 2460: IPv6 specification.
214
216 This page is part of release 3.25 of the Linux man-pages project. A
217 description of the project, and information about reporting bugs, can
218 be found at http://www.kernel.org/doc/man-pages/.
219Linux 2009-02-28 IPV6(7)