INET6(4)                NetBSD Kernel Interfaces 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 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:
     o   A specific bind on an AF_INET6 socket (bind(2) with an address
         specified) should accept IPv6 traffic to that address only.
     o   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.
     o   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 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 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.

NetBSD 5.0_STABLE              January 29, 1999              NetBSD 5.0_STABLE
