INET6(4) BSD Kernel Interfaces Manual INET6(4)NAMEinet6 — Internet protocol version 6 family
SYNOPSIS
#include <sys/types.h>
#include <netinet/in.h>
DESCRIPTION
The inet6 family is an updated version of inet(4) family. While inet(4)
implements Internet Protocol version 4, inet6 implements Internet Proto‐
col version 6.
inet6 is a collection of protocols layered atop the Internet Protocol
version 6 (IPv6) transport layer, and using 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 byte‐
order. The include file <netinet/in.h> defines this address as a dis‐
criminated union.
Sockets bound to the inet6 family use the following addressing structure:
struct sockaddr_in6 {
uint8_t sin6_len;
sa_family_t sin6_family;
in_port_t sin6_port;
uint32_t sin6_flowinfo;
struct in6_addr sin6_addr;
uint32_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 addresses, like link-local or site-
local addresses. A scoped address is ambiguous to the kernel, if it is
specified without a scope identifier. To manipulate scoped addresses
properly from the userland, programs must use the advanced API defined in
RFC 2292. A compact description of the advanced API is available in
ip6(4). If a scoped address is specified without an 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.
The KAME implementation supports an extended numeric IPv6 address nota‐
tion for link-local addresses, like “fe80::1%de0” to specify “fe80::1 on
de0 interface”. This notation is supported by getaddrinfo(3) and
getnameinfo(3). Some of normal userland programs, such as telnet(1) or
ftp(1), are able to use this notation. With special programs like
ping6(8), you can specify the outgoing interface by an extra command line
option to disambiguate scoped addresses.
Scoped addresses are handled specially in the kernel. In kernel struc‐
tures like routing tables or interface structures, a scoped address will
have its interface index embedded into the address. Therefore, the
address in some kernel structures is not the same as that on the wire.
The embedded index will become visible through a PF_ROUTE socket, kernel
memory accesses via kvm(3) and on some other occasions. HOWEVER, users
should never use the embedded form. For details please consult
http://www.kame.net/dev/cvsweb.cgi/kame/IMPLEMENTATION. Note that the
above URL describes the situation with the latest KAME tree, not the
NetBSD tree.
PROTOCOLS
The inet6 family comprises 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
By default, NetBSD does not route IPv4 traffic to AF_INET6 sockets. The
default behavior intentionally violates RFC 2553 for security reasons.
Listen to two sockets if you want to accept both IPv4 and IPv6 traffic.
IPv4 traffic may be routed with certain per-socket/per-node configura‐
tion, however, it is not recommended to do so. Consult ip6(4) for
details.
The behavior of AF_INET6 TCP/UDP socket is documented in RFC 2553. Basi‐
cally, it says this:
· A specific bind on an AF_INET6 socket (bind(2) with an address
specified) should accept IPv6 traffic to that address only.
· If you perform a wildcard bind 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 an IPv6 address like ::ffff:10.1.1.1. This is called an IPv4
mapped address.
· If there are both a wildcard bind AF_INET socket and a wildcard bind
AF_INET6 socket on one TCP/UDP port, they should behave separately.
IPv4 traffic should be routed to the AF_INET socket and IPv6 should
be routed to the AF_INET6 socket.
However, RFC 2553 does not define the ordering constraint between calls
to bind(2), nor how IPv4 TCP/UDP port numbers and IPv6 TCP/UDP port num‐
bers 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
sockets. It is recommended to listen to two sockets, one for AF_INET and
another for AF_INET6, when you would like to accept both IPv4 and IPv6
traffic.
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. Users are advised to
take care handling connections from IPv4 mapped address to AF_INET6 sock‐
ets.
SEE ALSOioctl(2), socket(2), sysctl(3), icmp6(4), intro(4), ip6(4), tcp(4),
udp(4)
Qing Li, Tatuya Jinmei, and Keiichi Shima, IPv6 Core Protocols
Implementation, Morgan Kaufmann, 2006.
Qing Li, Tatuya Jinmei, and Keiichi Shima, IPv6 Advanced Protocols
Implementation, Morgan Kaufmann, 2007.
STANDARDS
Tatuya Jinmei and Atsushi Onoe, An Extension of Format for IPv6 Scoped
Addresses, internet draft, draft-ietf-ipngwg-scopedaddr-format-02.txt,
June 2000, work in progress material.
HISTORY
The inet6 protocol interfaces are defined in RFC 2553 and RFC 2292. The
implementation described herein appeared in the 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.
Users are suggested to implement “version independent” code as much as
possible, as you will need to support both inet(4) and inet6.
BSD March 10, 2010 BSD
