.\"	$OpenBSD: inet6.4,v 1.29 2009/12/13 15:48:21 sobrado Exp $
.\"	$KAME: inet6.4,v 1.19 2000/11/24 10:13:18 itojun Exp $
.\"
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.Dd $Mdocdate: December 13 2009 $
.Dt INET6 4
.Os
.Sh NAME
.Nm inet6
.Nd Internet protocol version 6 family
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <netinet/in.h>
.Sh DESCRIPTION
The
.Nm
family is an updated version of the
.Xr inet 4
family.
While
.Xr inet 4
implements Internet Protocol version 4,
.Nm
implements Internet Protocol version 6.
.Pp
.Nm
is a collection of protocols layered atop the
.Em Internet Protocol version 6
.Pq Tn IPv6
transport layer, and utilizing the IPv6 address format.
The
.Nm
family provides protocol support for the
.Dv SOCK_STREAM ,
.Dv SOCK_DGRAM ,
and
.Dv SOCK_RAW
socket types; the
.Dv SOCK_RAW
interface provides access to the
.Tn IPv6
protocol.
.Sh ADDRESSING
IPv6 addresses are 16 byte quantities, stored in network standard byteorder.
The include file
.Aq Pa netinet/in.h
defines this address
as a discriminated union.
.Pp
Sockets bound to the
.Nm
family utilize the following addressing structure:
.Bd -literal -offset indent
struct sockaddr_in6 {
	u_int8_t	sin6_len;
	sa_family_t	sin6_family;
	in_port_t	sin6_port;
	u_int32_t	sin6_flowinfo;
	struct in6_addr	sin6_addr;
	u_int32_t	sin6_scope_id;
};
.Ed
.Pp
Sockets may be created with the local address
.Dq Dv ::
.Po
which is equal to IPv6 address
.Dv 0:0:0:0:0:0:0:0
.Pc
to effect
.Dq wildcard
matching on incoming messages.
.Pp
The IPv6 specification defines scoped address,
like link-local or site-local address.
A scoped address is ambiguous to the kernel,
if it is specified without a scope identifier.
To manipulate scoped addresses properly from userland,
programs must use the advanced API defined in RFC 2292.
A compact description of the advanced API is available in
.Xr ip6 4 .
If scoped addresses are specified without explicit scope,
the kernel may raise an error.
Note that scoped addresses are not for daily use at this moment,
both from a specification and an implementation point of view.
.Pp
KAME implementation supports extended numeric IPv6 address notation
for link-local addresses,
like
.Dq Li fe80::1%de0
to specify
.Do
.Li fe80::1
on
.Li de0
interface
.Dc .
The notation is supported by
.Xr getaddrinfo 3
and
.Xr getnameinfo 3 .
Some normal userland programs, such as
.Xr telnet 1
or
.Xr ftp 1 ,
are able to use the notation.
With special programs
like
.Xr ping6 8 ,
an outgoing interface can be specified with an extra command line option
to disambiguate scoped addresses.
.Pp
Scoped addresses are handled specially in the kernel.
In the kernel structures like routing tables or interface structure,
scoped addresses will have their interface index embedded into the address.
Therefore,
the address on some of the kernel structure is not the same as that on the wire.
The embedded index will become visible on
.Dv PF_ROUTE
socket, kernel memory accesses via
.Xr kvm 3
and some other occasions.
HOWEVER, users should never use the embedded form.
For details please consult
.Pa http://www.kame.net/dev/cvsweb2.cgi/kame/IMPLEMENTATION .
Note that the above URL describes the situation with the latest KAME tree,
not the
.Ox
tree.
.Sh PROTOCOLS
The
.Nm
family is comprised of the
.Tn IPv6
network protocol, Internet Control
Message Protocol version 6
.Pq Tn ICMPv6 ,
Transmission Control Protocol
.Pq Tn TCP ,
and User Datagram Protocol
.Pq Tn UDP .
.Tn TCP
is used to support the
.Dv SOCK_STREAM
abstraction while
.Tn UDP
is used to support the
.Dv SOCK_DGRAM
abstraction.
Note that
.Tn TCP
and
.Tn UDP
are common to
.Xr inet 4
and
.Nm inet6 .
A raw interface to
.Tn IPv6
is available
by creating an Internet socket of type
.Dv SOCK_RAW .
The
.Tn ICMPv6
message protocol is accessible from a raw socket.
.\" .Pp
.\" The 128-bit IPv6 address contains both network and host parts.
.\" However, direct examination of addresses is discouraged.
.\" For those programs which absolutely need to break addresses
.\" into their component parts, the following
.\" .Xr ioctl 2
.\" commands are provided for a datagram socket in the
.\" .Nm
.\" domain; they have the same form as the
.\" .Dv SIOCIFADDR
.\" command (see
.\" .Xr intro 4 ) .
.\" .Pp
.\" .Bl -tag -width SIOCSIFNETMASK
.\" .It Dv SIOCSIFNETMASK
.\" Set interface network mask.
.\" The network mask defines the network part of the address;
.\" if it contains more of the address than the address type would indicate,
.\" then subnets are in use.
.\" .It Dv SIOCGIFNETMASK
.\" Get interface network mask.
.\" .El
.Ss Interaction between IPv4/v6 sockets
.Ox
does not route IPv4 traffic to an
.Dv AF_INET6
socket,
for security reasons.
If both IPv4 and IPv6 traffic need to be accepted, listen on two sockets.
.Pp
The behavior of
.Dv AF_INET6
TCP/UDP socket is documented in RFC 2553.
Basically, it says the following:
.Pp
.Bl -bullet -compact
.It
A specific bind to an
.Dv AF_INET6
socket
.Po
.Xr bind 2
with address specified
.Pc
should accept IPv6 traffic to that address only.
.It
If a wildcard bind is performed on an
.Dv AF_INET6
socket
.Po
.Xr bind 2
to IPv6 address
.Li ::
.Pc ,
and there is no wildcard bind
.Dv AF_INET
socket on that TCP/UDP port, IPv6 traffic as well as IPv4 traffic
should be routed to that
.Dv AF_INET6
socket.
IPv4 traffic should be seen as if it came from IPv6 address like
.Li ::ffff:10.1.1.1 .
This is called IPv4 mapped address.
.It
If there are both wildcard bind
.Dv AF_INET
socket and wildcard bind
.Dv AF_INET6
socket on one TCP/UDP port, they should behave separately.
IPv4 traffic should be routed to
.Dv AF_INET
socket and IPv6 should be routed to
.Dv AF_INET6
socket.
.El
.Pp
However, RFC 2553 does not define the constraint between the order of
.Xr bind 2 ,
nor how IPv4 TCP/UDP port numbers and IPv6 TCP/UDP port numbers
relate to each other
.Po
should they be integrated or separated
.Pc .
Implemented behavior is very different from kernel to kernel.
Therefore, it is unwise to rely too much upon the behavior of
.Dv AF_INET6
wildcard bind socket.
It is recommended to listen to two sockets, one for
.Dv AF_INET
and another for
.Dv AF_INET6 ,
if both IPv4 and IPv6 traffic are to be accepted.
.Pp
It should also be noted that
malicious parties can take advantage of the complexity presented above,
and are able to bypass access control,
if the target node routes IPv4 traffic to
.Dv AF_INET6
socket.
Caution should be taken when handling connections
from IPv4 mapped addresses to
.Dv AF_INET6
sockets.
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr socket 2 ,
.Xr sysctl 3 ,
.Xr icmp6 4 ,
.Xr intro 4 ,
.Xr ip6 4 ,
.Xr tcp 4 ,
.Xr udp 4
.Sh STANDARDS
.Rs
.%A Tatsuya Jinmei
.%A Atsushi Onoe
.%T "An Extension of Format for IPv6 Scoped Addresses"
.%R internet draft
.%D June 2000
.%N draft-ietf-ipngwg-scopedaddr-format-02.txt
.%O work in progress material
.Re
.Sh HISTORY
The
.Nm
protocol interface is defined in RFC 2553 and RFC 2292.
The implementation described herein appeared in WIDE/KAME project.
.Sh BUGS
The IPv6 support is subject to change as the Internet protocols develop.
Users should not depend on details of the current implementation,
but rather the services exported.
.Pp
.Dq Version independent
code should be implemented as much as possible in order to support both
.Xr inet 4
and
.Nm inet6 .