ipv6 - phpMan

IPV6(7) Linux Programmer’s Manual IPV6(7)

NAME
ipv6, PF_INET6 - Linux IPv6 protocol implementation

SYNOPSIS
#include <sys/socket.h>
#include <netinet/in.h>

tcp6_socket = socket(PF_INET6, SOCK_STREAM, 0);
raw6_socket = socket(PF_INET6, SOCK_RAW, protocol);
udp6_socket = socket(PF_INET6, SOCK_DGRAM, protocol);

DESCRIPTION
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 ip(7) v4 API. 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 order.

The IPv6 loopback address (::1) is available in the global in6addr_loopback vari-
able. 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 only to support this API type to support
both protocols. This is handled transparently by the address handling functions in
libc.

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’ll be mapped to v6.

ADDRESS FORMAT
struct sockaddr_in6 {
u_int16_t sin6_family;/* AF_INET6 */
u_int16_t sin6_port;/* port number */
u_int32_t sin6_flowinfo;/* IPv6 flow information */
struct in6_addr sin6_addr;/* IPv6 address */
u_int32_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 128bit IPv6
address. sin6_scope_id is an id of depending of 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, sepa-
rated 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.

SOCKET OPTIONS
IPv6 supports some protocol specific socket options that can be set with setsock-
opt(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_UNICAST_HOPS
Set the unicast hop limit for the socket. Argument is an pointer to an inte-
ger. -1 in the value means use the route default, otherwise it should be
between 0 and 255.

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 an pointer to
an interface index (see netdevice(7)) in an integer.

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 a integer containing AF_INET. This is useful to pass v4-mapped
sockets as filedescriptors to programs that don’t know how to deal with the
IPv6 API.

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 extension
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 inte-
ger 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. Ar-
gument is a pointer to a boolean value.

IPV6_MULTICAST_LOOP
Control whether the socket sees multicast packets that is has send itself.
Argument is a pointer to boolean.

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_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 all forwarded packets containing an router alert option to this socket.
Only allowed for datagram sockets and for root. Argument is a pointer to
boolean.

VERSIONS
The older libinet6 libc5 based IPv6 API implementation for Linux is not described
here and may vary in details.

Linux 2.4 will break binary compatibility for the sockaddr_in6 for 64bit hosts by
changing the alignment of in6_addr and adding an additional sin6_scope_id field.
The kernel interfaces stay compatible, but a program including sockaddr_in6 or
in6_addr into other structures may not be. This is not a problem for 32bit 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.

PORTING NOTES
The sockaddr_in6 structure is bigger than the generic sockaddr. Programs that as-
sume that all address types can be stored safely in a struct sockaddr need to be
changed to use struct sockaddr_storage for that instead.

BUGS
The IPv6 extended API as in RFC2292 is currently only partly implemented; although
the 2.2 kernel has near complete support for receiving options, the macros for gen-
erating 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.