| INET6(4) |
AerieBSD 1.0 Refernce Manual |
INET6(4) |
NAME
inet6 —
Internet protocol version 6 family
SYNOPSIS
#include <sys/types.h>
#include <netinet/in.h>
DESCRIPTION
The
inet6
family is an updated version of the
inet(4)
family.
While
inet(4)
implements Internet Protocol version 4,
inet6
implements Internet Protocol version 6.
inet6
is a collection of protocols layered atop the
Internet Protocol version 6
(IPv6)
transport layer, and utilizing the IPv6 address format.
The
inet6
family provides protocol support for the
SOCK_STREAM,
SOCK_DGRAM,
and
SOCK_RAW
socket types; the
SOCK_RAW
interface provides access to the
IPv6
protocol.
ADDRESSING
IPv6 addresses are 16 byte quantities, stored in network standard byteorder.
The include file
‹netinet/in.h›
defines this address
as a discriminated union.
Sockets bound to the
inet6
family utilize the following addressing structure:
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;
};
Sockets may be created with the local address
“”::
(
which is equal to IPv6 address
0:0:0:0:0:0:0:0
)
to effect
“wildcard”
matching on incoming messages.
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
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.
KAME implementation supports extended numeric IPv6 address notation
for link-local addresses,
like
“fe80::1%de0”
to specify
“
fe80::1
on
de0
interface
”.
The notation is supported by
getaddrinfo(3)
and
getnameinfo(3).
Some normal userland programs, such as
telnet(1)
or
ftp(1),
are able to use the notation.
With special programs
like
ping6(8),
an outgoing interface can be specified with an extra command line option
to disambiguate scoped addresses.
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
PF_ROUTE
socket, kernel memory accesses via
kvm(3)
and some other occasions.
HOWEVER, users should never use the embedded form.
For details please consult
http://www.kame.net/dev/cvsweb2.cgi/kame/IMPLEMENTATION.
Note that the above URL describes the situation with the latest KAME tree,
not the
OpenBSD
tree.
PROTOCOLS
The
inet6
family is comprised of the
IPv6
network protocol, Internet Control
Message Protocol version 6
(ICMPv6),
Transmission Control Protocol
(TCP),
and User Datagram Protocol
(UDP).
TCP
is used to support the
SOCK_STREAM
abstraction while
UDP
is used to support the
SOCK_DGRAM
abstraction.
Note that
TCP
and
UDP
are common to
inet(4)
and
inet6.
A raw interface to
IPv6
is available
by creating an Internet socket of type
SOCK_RAW.
The
ICMPv6
message protocol is accessible from a raw socket.
Interaction between IPv4/v6 sockets
OpenBSD
does not route IPv4 traffic to an
AF_INET6
socket,
for security reasons.
If both IPv4 and IPv6 traffic need to be accepted, listen on two sockets.
The behavior of
AF_INET6
TCP/UDP socket is documented in RFC 2553.
Basically, it says the following:
-
A specific bind to an
AF_INET6
socket
(
bind(2)
with address specified
)
should accept IPv6 traffic to that address only.
-
If a wildcard bind is performed on an
AF_INET6
socket
(
bind(2)
to IPv6 address
::
),
and there is no wildcard bind
AF_INET
socket on that TCP/UDP port, IPv6 traffic as well as IPv4 traffic
should be routed to that
AF_INET6
socket.
IPv4 traffic should be seen as if it came from IPv6 address like
::ffff:10.1.1.1.
This is called IPv4 mapped address.
-
If there are both wildcard bind
AF_INET
socket and wildcard bind
AF_INET6
socket on one TCP/UDP port, they should behave separately.
IPv4 traffic should be routed to
AF_INET
socket and IPv6 should be routed to
AF_INET6
socket.
However, RFC 2553 does not define the constraint between the order of
bind(2),
nor how IPv4 TCP/UDP port numbers and IPv6 TCP/UDP port numbers
relate to each other
(
should they be integrated or separated
).
Implemented behavior is very different from kernel to kernel.
Therefore, it is unwise to rely too much upon the behavior of
AF_INET6
wildcard bind socket.
It is recommended to listen to two sockets, one for
AF_INET
and another for
AF_INET6,
if both IPv4 and IPv6 traffic are to be accepted.
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
AF_INET6
socket.
Caution should be taken when handling connections
from IPv4 mapped addresses to
AF_INET6
sockets.
SEE ALSO
ioctl(2),
socket(2),
sysctl(3),
icmp6(4),
intro(4),
ip6(4),
tcp(4),
udp(4)
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
HISTORY
The
inet6
protocol interface is defined in RFC 2553 and RFC 2292.
The implementation described herein appeared in WIDE/KAME project.
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.
“Version independent”
code should be implemented as much as possible in order to support both
inet(4)
and
inet6.
| AerieBSD 1.0 Reference Manual |
August 26 2008 |
INET6(4) |