NAME | SYNOPSIS | DESCRIPTION | VERSIONS | NOTES | BUGS | SEE ALSO | COLOPHON
IPV6(7) Linux Programmer's Manual IPV6(7)
ipv6, AF_INET6 - Linux IPv6 protocol implementation
#include <sys/socket.h>
#include <netinet/in.h>
tcp6_socket = socket(AF_INET6, SOCK_STREAM, 0);
raw6_socket = socket(AF_INET6, SOCK_RAW, protocol);
udp6_socket = socket(AF_INET6, SOCK_DGRAM, protocol);
Linux 2.2 optionally implements the Internet Protocol, version 6. This man
page contains a description of the IPv6 basic API as implemented by the Linux
kernel and glibc 2.1. The interface is based on the BSD sockets interface;
see socket(7).
The IPv6 API aims to be mostly compatible with the IPv4 API (see ip(7)). Only
differences are described in this man page.
To bind an AF_INET6 socket to any process, the local address should be copied
from the in6addr_any variable which has in6_addr type. In static
initializations, IN6ADDR_ANY_INIT may also be used, which expands to a
constant expression. Both of them are in network byte order.
The IPv6 loopback address (::1) is available in the global in6addr_loopback
variable. For initializations, IN6ADDR_LOOPBACK_INIT should be used.
IPv4 connections can be handled with the v6 API by using the v4-mapped-on-v6
address type; thus a program only needs to support this API type to support
both protocols. This is handled transparently by the address handling
functions in the C library.
IPv4 and IPv6 share the local port space. When you get an IPv4 connection or
packet to a IPv6 socket, its source address will be mapped to v6 and it will
be mapped to v6.
struct sockaddr_in6 {
sa_family_t sin6_family; /* AF_INET6 */
in_port_t sin6_port; /* port number */
uint32_t sin6_flowinfo; /* IPv6 flow information */
struct in6_addr sin6_addr; /* IPv6 address */
uint32_t sin6_scope_id; /* Scope ID (new in 2.4) */
};
struct in6_addr {
unsigned char s6_addr[16]; /* IPv6 address */
};
sin6_family is always set to AF_INET6; sin6_port is the protocol port (see
sin_port in ip(7)); sin6_flowinfo is the IPv6 flow identifier; sin6_addr is
the 128-bit IPv6 address. sin6_scope_id is an ID depending on the scope of
the address. It is new in Linux 2.4. Linux only supports it for link scope
addresses, in that case sin6_scope_id contains the interface index (see
netdevice(7))
IPv6 supports several address types: unicast to address a single host,
multicast to address a group of hosts, anycast to address the nearest member
of a group of hosts (not implemented in Linux), IPv4-on-IPv6 to address a IPv4
host, and other reserved address types.
The address notation for IPv6 is a group of 16 2-digit hexadecimal numbers,
separated with a ':'. "::" stands for a string of 0 bits. Special addresses
are ::1 for loopback and ::FFFF:<IPv4 address> for IPv4-mapped-on-IPv6.
The port space of IPv6 is shared with IPv4.
IPv6 supports some protocol-specific socket options that can be set with
setsockopt(2) and read with getsockopt(2). The socket option level for IPv6
is IPPROTO_IPV6. A boolean integer flag is zero when it is false, otherwise
true.
IPV6_ADDRFORM
Turn an AF_INET6 socket into a socket of a different address family.
Only AF_INET is currently supported for that. It is only allowed for
IPv6 sockets that are connected and bound to a v4-mapped-on-v6 address.
The argument is a pointer to an integer containing AF_INET. This is
useful to pass v4-mapped sockets as file descriptors to programs that
don't know how to deal with the IPv6 API.
IPV6_ADD_MEMBERSHIP, IPV6_DROP_MEMBERSHIP
Control membership in multicast groups. Argument is a pointer to a
struct ipv6_mreq structure.
IPV6_MTU
Set the MTU to be used for the socket. The MTU is limited by the
device MTU or the path mtu when path mtu discovery is enabled.
Argument is a pointer to integer.
IPV6_MTU_DISCOVER
Control path mtu discovery on the socket. See IP_MTU_DISCOVER in ip(7)
for details.
IPV6_MULTICAST_HOPS
Set the multicast hop limit for the socket. Argument is a pointer to
an integer. -1 in the value means use the route default, otherwise it
should be between 0 and 255.
IPV6_MULTICAST_IF
Set the device for outgoing multicast packets on the socket. This is
only allowed for SOCK_DGRAM and SOCK_RAW socket. The argument is a
pointer to an interface index (see netdevice(7)) in an integer.
IPV6_MULTICAST_LOOP
Control whether the socket sees multicast packets that it has send
itself. Argument is a pointer to boolean.
IPV6_PKTINFO
Set delivery of the IPV6_PKTINFO control message on incoming datagrams.
Only allowed for SOCK_DGRAM or SOCK_RAW sockets. Argument is a pointer
to a boolean value in an integer.
IPV6_RTHDR, IPV6_AUTHHDR, IPV6_DSTOPS, IPV6_HOPOPTS, IPV6_FLOWINFO,
IPV6_HOPLIMIT
Set delivery of control messages for incoming datagrams containing ex-
tension headers from the received packet. IPV6_RTHDR delivers the
routing header, IPV6_AUTHHDR delivers the authentication header,
IPV6_DSTOPTS delivers the destination options, IPV6_HOPOPTS delivers
the hop options, IPV6_FLOWINFO delivers an integer containing the flow
ID, IPV6_HOPLIMIT delivers an integer containing the hop count of the
packet. The control messages have the same type as the socket option.
All these header options can also be set for outgoing packets by
putting the appropriate control message into the control buffer of
sendmsg(2). Only allowed for SOCK_DGRAM or SOCK_RAW sockets. Argument
is a pointer to a boolean value.
IPV6_RECVERR
Control receiving of asynchronous error options. See IP_RECVERR in
ip(7) for details. Argument is a pointer to boolean.
IPV6_ROUTER_ALERT
Pass forwarded packets containing a router alert hop-by-hop option to
this socket. Only allowed for SOCK_RAW sockets. The tapped packets
are not forwarded by the kernel, it is the user's responsibility to
send them out again. Argument is a pointer to an integer. A positive
integer indicates a router alert option value to intercept. Packets
carrying a router alert option with a value field containing this inte-
ger will be delivered to the socket. A negative integer disables de-
livery of packets with router alert options to this socket.
IPV6_UNICAST_HOPS
Set the unicast hop limit for the socket. Argument is a pointer to an
integer. -1 in the value means use the route default, otherwise it
should be between 0 and 255.
IPV6_V6ONLY (since Linux 2.4.21 and 2.6)
If this flag is set to true (non-zero), then the socket is restricted
to sending and receiving IPv6 packets only. In this case, an IPv4 and
an IPv6 application can bind to a single port at the same time.
If this flag is set to false (zero), then the socket can be used to
send and receive packets to and from an IPv6 address or an IPv4-mapped
IPv6 address.
The argument is a pointer to a boolean value in an integer.
The default value for this flag is defined by the contents of the file
/proc/sys/net/ipv6/bindv6only. The default value for that file is 0
(false).
The older libinet6 libc5 based IPv6 API implementation for Linux is not de-
scribed here and may vary in details.
Linux 2.4 will break binary compatibility for the sockaddr_in6 for 64-bit
hosts by changing the alignment of in6_addr and adding an additional
sin6_scope_id field. The kernel interfaces stay compatible, but a program in-
cluding sockaddr_in6 or in6_addr into other structures may not be. This is
not a problem for 32-bit hosts like i386.
The sin6_flowinfo field is new in Linux 2.4. It is transparently passed/read
by the kernel when the passed address length contains it. Some programs that
pass a longer address buffer and then check the outgoing address length may
break.
The sockaddr_in6 structure is bigger than the generic sockaddr. Programs that
assume that all address types can be stored safely in a struct sockaddr need
to be changed to use struct sockaddr_storage for that instead.
The IPv6 extended API as in RFC 2292 is currently only partly implemented; al-
though the 2.2 kernel has near complete support for receiving options, the
macros for generating IPv6 options are missing in glibc 2.1.
IPSec support for EH and AH headers is missing.
Flow label management is not complete and not documented here.
This man page is not complete.
cmsg(3), ip(7)
RFC 2553: IPv6 BASIC API. Linux tries to be compliant to this.
RFC 2460: IPv6 specification.
This page is part of release 3.23 of the Linux man-pages project. A descrip-
tion of the project, and information about reporting bugs, can be found at
http://www.kernel.org/doc/man-pages/.
Linux 2009-02-28 IPV6(7)