1ipv6(7) Miscellaneous Information Manual ipv6(7)
2
6 ipv6 - 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 ex‐
28 pands to a constant expression. Both of them are in network byte or‐
29 der.
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 needs to support only this API type
37 to support both protocols. This is handled transparently by the ad‐
38 dress 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 an IPv6 socket, its source address will be mapped to
42 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 Linux 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 sup‐
61 ports it only for link-local 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 an IPv4 host, and other reserved address types.
68 The address notation for IPv6 is a group of 8 4-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 allowed only 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.
94 IPV6_MTU
96 getsockopt(): Retrieve the current known path MTU of the current
97 socket. Valid only when the socket has been connected. Returns
98 an integer.
99 setsockopt(): Set the MTU to be used for the socket. The MTU is
101 limited by the device MTU or the path MTU when path MTU discov‐
102 ery is enabled. Argument is a pointer to integer.
103 IPV6_MTU_DISCOVER
105 Control path-MTU discovery on the socket. See IP_MTU_DISCOVER
106 in ip(7) for details.
107 IPV6_MULTICAST_HOPS
109 Set the multicast hop limit for the socket. Argument is a
110 pointer to an integer. -1 in the value means use the route de‐
111 fault, otherwise it should be between 0 and 255.
112 IPV6_MULTICAST_IF
114 Set the device for outgoing multicast packets on the socket.
115 This is allowed only for SOCK_DGRAM and SOCK_RAW socket. The
116 argument is a pointer to an interface index (see netdevice(7))
117 in an integer.
118 IPV6_MULTICAST_LOOP
120 Control whether the socket sees multicast packets that it has
121 send itself. Argument is a pointer to boolean.
122 IPV6_RECVPKTINFO (since Linux 2.6.14)
124 Set delivery of the IPV6_PKTINFO control message on incoming
125 datagrams. Such control messages contain a struct in6_pktinfo,
126 as per RFC 3542. Allowed only for SOCK_DGRAM or SOCK_RAW sock‐
127 ets. Argument is a pointer to a boolean value in an integer.
128 IPV6_RTHDR, IPV6_AUTHHDR, IPV6_DSTOPTS, IPV6_HOPOPTS, IPV6_FLOWINFO,
130 IPV6_HOPLIMIT
131 Set delivery of control messages for incoming datagrams contain‐
132 ing extension headers from the received packet. IPV6_RTHDR de‐
133 livers the routing header, IPV6_AUTHHDR delivers the authentica‐
134 tion header, IPV6_DSTOPTS delivers the destination options,
135 IPV6_HOPOPTS delivers the hop options, IPV6_FLOWINFO delivers an
136 integer containing the flow ID, IPV6_HOPLIMIT delivers an inte‐
137 ger containing the hop count of the packet. The control mes‐
138 sages have the same type as the socket option. All these header
139 options can also be set for outgoing packets by putting the ap‐
140 propriate control message into the control buffer of sendmsg(2).
141 Allowed only for SOCK_DGRAM or SOCK_RAW sockets. Argument is a
142 pointer to a boolean value.
143 IPV6_RECVERR
145 Control receiving of asynchronous error options. See IP_RECVERR
146 in ip(7) for details. Argument is a pointer to boolean.
147 IPV6_ROUTER_ALERT
149 Pass forwarded packets containing a router alert hop-by-hop op‐
150 tion to this socket. Allowed only for SOCK_RAW sockets. The
151 tapped packets are not forwarded by the kernel, it is the user's
152 responsibility to send them out again. Argument is a pointer to
153 an integer. A positive integer indicates a router alert option
154 value to intercept. Packets carrying a router alert option with
155 a value field containing this integer will be delivered to the
156 socket. A negative integer disables delivery of packets with
157 router alert options to this socket.
158 IPV6_UNICAST_HOPS
160 Set the unicast hop limit for the socket. Argument is a pointer
161 to an integer. -1 in the value means use the route default,
162 otherwise it should be between 0 and 255.
163 IPV6_V6ONLY (since Linux 2.4.21 and 2.6)
165 If this flag is set to true (nonzero), then the socket is re‐
166 stricted to sending and receiving IPv6 packets only. In this
167 case, an IPv4 and an IPv6 application can bind to a single port
168 at the same time.
169 If this flag is set to false (zero), then the socket can be used
171 to send and receive packets to and from an IPv6 address or an
172 IPv4-mapped IPv6 address.
173 The argument is a pointer to a boolean value in an integer.
175 The default value for this flag is defined by the contents of
177 the file /proc/sys/net/ipv6/bindv6only. The default value for
178 that file is 0 (false).
179
181 ENODEV The user tried to bind(2) to a link-local IPv6 address, but the
182 sin6_scope_id in the supplied sockaddr_in6 structure is not a
183 valid interface index.
184
186 Linux 2.4 will break binary compatibility for the sockaddr_in6 for
187 64-bit hosts by changing the alignment of in6_addr and adding an addi‐
188 tional sin6_scope_id field. The kernel interfaces stay compatible, but
189 a program including sockaddr_in6 or in6_addr into other structures may
190 not be. This is not a problem for 32-bit hosts like i386.
191 The sin6_flowinfo field is new in Linux 2.4. It is transparently
193 passed/read by the kernel when the passed address length contains it.
194 Some programs that pass a longer address buffer and then check the out‐
195 going address length may break.
196
198 The sockaddr_in6 structure is bigger than the generic sockaddr. Pro‐
199 grams that assume that all address types can be stored safely in a
200 struct sockaddr need to be changed to use struct sockaddr_storage for
201 that instead.
202 SOL_IP, SOL_IPV6, SOL_ICMPV6, and other SOL_* socket options are non‐
204 portable variants of IPPROTO_*. See also ip(7).
205
207 The IPv6 extended API as in RFC 2292 is currently only partly imple‐
208 mented; although the 2.2 kernel has near complete support for receiving
209 options, the macros for generating IPv6 options are missing in glibc
210 2.1.
211 IPSec support for EH and AH headers is missing.
213 Flow label management is not complete and not documented here.
215 This man page is not complete.
217
219 cmsg(3), ip(7)
220 RFC 2553: IPv6 BASIC API; Linux tries to be compliant to this.
222 RFC 2460: IPv6 specification.
223Linux man-pages 6.04 2023-02-05 ipv6(7)