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NAME    [Toc]    [Back]

     inet6 - Internet protocol version 6 family

SYNOPSIS    [Toc]    [Back]

     #include <sys/types.h>
     #include <netinet/in.h>

DESCRIPTION    [Toc]    [Back]

     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
     version 6 (IPv6) transport layer, and utilizing the IPv6 address format.
     The  inet6  family  provides  protocol   support   for   the
     SOCK_DGRAM,  and  SOCK_RAW socket types; the SOCK_RAW interface provides
     access to the IPv6 protocol.

ADDRESSING    [Toc]    [Back]

     IPv6 addresses are 16 byte  quantities,  stored  in  network
standard byteorder.
  The include file <netinet/in.h> defines this address
as a discriminated

     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

     The IPv6 specification defines scoped address, like link-local or sitelocal
 address.  A scoped address is ambiguous to the kernel,
if it is
     specified  without a scope identifier.  To manipulate scoped
     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)
     getnameinfo(3).  Some normal userland programs, such as telnet(1) or
     ftp(1), are able to use the notation.  With special programs
     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.
     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.
     users  should  never  use  the  embedded  form.  For details
please consult
Note that the
     above URL describes the situation with the latest KAME tree,
not the
     OpenBSD tree.

PROTOCOLS    [Toc]    [Back]

     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.
The particular
 behavior in RFC 2553 is intentionally omitted for  security reasons
     presented  above.   If both IPv4 and IPv6 traffic need to be
accepted, listen
 to two sockets.

     The behavior of AF_INET6 TCP/UDP socket is documented in RFC
2553.  Basically,
 it says the following:

     +o    A specific bind to an AF_INET6 socket (bind(2) with address
         specified) should accept IPv6 traffic  to  that  address
     +o    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:  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
         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
     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

SEE ALSO    [Toc]    [Back]

     ioctl(2), socket(2), sysctl(3), icmp6(4), intro(4),  ip6(4),

STANDARDS    [Toc]    [Back]

     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    [Toc]    [Back]

     The  inet6 protocol interface is defined in RFC 2553 and RFC
2292.  The
     implementation described herein appeared in  WIDE/KAME  project.

BUGS    [Toc]    [Back]

     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.

OpenBSD     3.6                        January      29,      1999
[ Back ]
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