INET6(4) BSD Programmer's 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 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 byte-
order. The include file <netinet/in.h> defines this address as a dis-
criminated union.
Sockets bound to the inet6 family utilize the following addressing struc-
ture:
struct sockaddr_in6 {
u_int8_t sin6_len;
u_int8_t sin6_family;
u_int16_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.
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 scope identifier. To manipulate scoped addresses properly from
the userland, programs must use advanced API defined in RFC2292. Compact
description on the advanced API is available in ip6(4). If scoped ad-
dresses are specified without explicit scope, the kernel may raise error.
Note that scoped addresses are not for daily use at this moment, both
from specification and 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 of normal userland programs, such as telnet(1) or
ftp(1), are able to use the notation. With special programs like
ping6(8), you can specify outgoing interface by extra command line op-
tion 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 its 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
IMPLEMENTATION supplied with KAME kit.
PROTOCOLS
The inet6 family is comprised of the IPv6 network protocol, Internet Con-
trol 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 ab-
straction. 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
The behavior of AF_INET6 TCP/UDP socket is documented in RFC2553. Basi-
cally, it says as follows:
o Specific bind on AF_INET6 socket (bind(2) with address specified)
should accept IPv6 traffic to that address only.
o If you perform wildcard bind on 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.
o 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, RFC2553 does not define the constraint between the order of
bind(2), nor how IPv4 TCP/UDP port number and IPv6 TCP/UDP port number
relate each other (should they be integrated or separated). Implemented
behavior is very different across kernel to kernel. Therefore, it is un-
wise 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, 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 caution handling connections from IPv4 mapped address to AF_INET6
sockets.
SEE ALSOioctl(2), socket(2), sysctl(3), icmp6(4), intro(4), ip6(4), tcp(4),
ttcp(4), udp(4)STANDARDS
Tatsuya 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 interface are defined in RFC2553 and RFC2292. 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.
Users are suggested to implement ``version independent'' code as much as
possible, as you will need to support both inet(4) and inet6.
KAME January 29, 1999 2
