INET6(4)                  OpenBSD Programmer's 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 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;
                   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.

     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 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 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
     sys/netinet6/IMPLEMENTATION.

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.

     Because of the above, OpenBSD does not route IPv4 traffic to AF_INET6
     socket.  The particular behavior in RFC2553 is intentionally omitted for
     security reasons presented above.  If you need to accept both IPv4 and
     IPv6 traffic, listen to two sockets.

SEE ALSO
     ioctl(2), socket(2), sysctl(3), icmp6(4), intro(4), ip6(4), tcp(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.

OpenBSD 2.9                    January 29, 1999                              2
