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IPV6(7)                    Linux Programmer's Manual                   IPV6(7)

NAME
       ipv6, PF_INET6 - Linux IPv6 protocol implementation

SYNOPSIS
       #include <sys/socket.h>
       #include <netinet/in.h>

       tcp6_socket = socket(PF_INET6, SOCK_STREAM, 0);
       raw6_socket = socket(PF_INET6, SOCK_RAW, protocol);
       udp6_socket = socket(PF_INET6, SOCK_DGRAM, protocol);

DESCRIPTION
       Linux 2.2 optionally implements the Internet Protocol, version 6.  This
       man page contains a description of the IPv6 basic API as implemented by
       the  Linux  kernel  and  glibc  2.1.  The interface is based on the BSD
       sockets interface; see socket(7).

       The IPv6 API aims to be mostly compatible with the ip(7) v4 API.   Only
       differences are described in this man page.

       To  bind  an AF_INET6 socket to any process the local address should be
       copied from the in6addr_any  variable  which  has  in6_addr  type.   In
       static initializations IN6ADDR_ANY_INIT may also be used, which expands
       to a constant expression.  Both of them are in network order.

       The  IPv6  loopback  address  (::1)  is   available   in   the   global
       in6addr_loopback  variable.   For initializations IN6ADDR_LOOPBACK_INIT
       should be used.

       IPv4 connections can be handled with the v6 API by using the v4-mapped-
       on-v6  address type; thus a program only needs only to support this API
       type to support both protocols.  This is handled transparently  by  the
       address handling functions in libc.

       IPv4 and IPv6 share the local port space.  When you get an IPv4 connec-
       tion or packet to a IPv6 socket its source address will be mapped to v6
       and it will be mapped to v6.

   Address Format
           struct sockaddr_in6 {
               uint16_t        sin6_family;   /* AF_INET6 */
               uint16_t        sin6_port;     /* port number */
               uint32_t        sin6_flowinfo; /* IPv6 flow information */
               struct in6_addr sin6_addr;     /* IPv6 address */
               uint32_t        sin6_scope_id; /* Scope ID (new in 2.4) */
           };

           struct in6_addr {
               unsigned char   s6_addr[16];   /* IPv6 address */
           };

       sin6_family  is  always set to AF_INET6; sin6_port is the protocol port
       (see sin_port in ip(7)); sin6_flowinfo is  the  IPv6  flow  identifier;
       sin6_addr  is  the  128-bit  IPv6  address.   sin6_scope_id is an ID of
       depending of on the scope of the address.  It  is  new  in  Linux  2.4.
       Linux  only  supports  it  for  link  scope  addresses,  in  that  case
       sin6_scope_id contains the interface index (see netdevice(7))

       IPv6 supports several address types: unicast to address a single  host,
       multicast  to  address a group of hosts, anycast to address the nearest
       member of a group of hosts (not implemented in Linux), IPv4-on-IPv6  to
       address a IPv4 host, and other reserved address types.

       The address notation for IPv6 is a group of 16 2-digit hexadecimal num-
       bers, separated with a ':'.  "::" stands for a string of 0 bits.   Spe-
       cial  addresses  are  ::1  for  loopback  and ::FFFF:<IPv4 address> for
       IPv4-mapped-on-IPv6.

       The port space of IPv6 is shared with IPv4.

   Socket Options
       IPv6 supports some protocol-specific socket options  that  can  be  set
       with  setsockopt(2)  and  read  with  getsockopt(2).  The socket option
       level for IPv6 is IPPROTO_IPV6.  A boolean integer flag is zero when it
       is false, otherwise true.

       IPV6_ADDRFORM
              Turn  an  AF_INET6  socket  into a socket of a different address
              family.  Only AF_INET is currently supported for  that.   It  is
              only  allowed for IPv6 sockets that are connected and bound to a
              v4-mapped-on-v6 address.  The argument is a pointer to an  inte-
              ger  containing AF_INET.  This is useful to pass v4-mapped sock-
              ets as file descriptors to programs that don't know how to  deal
              with the IPv6 API.

       IPV6_ADD_MEMBERSHIP, IPV6_DROP_MEMBERSHIP
              Control  membership  in multicast groups.  Argument is a pointer
              to a struct ipv6_mreq structure.

       IPV6_MTU
              Set the MTU to be used for the socket.  The MTU  is  limited  by
              the  device  MTU  or  the  path  mtu  when path mtu discovery is
              enabled.  Argument is a pointer to integer.

       IPV6_MTU_DISCOVER
              Control path mtu discovery on the socket.   See  IP_MTU_DISCOVER
              in ip(7) for details.

       IPV6_MULTICAST_HOPS
              Set  the  multicast  hop  limit  for  the socket.  Argument is a
              pointer to an integer.  -1 in the  value  means  use  the  route
              default, otherwise it should be between 0 and 255.

       IPV6_MULTICAST_IF
              Set  the  device  for  outgoing multicast packets on the socket.
              This is only allowed for SOCK_DGRAM and  SOCK_RAW  socket.   The
              argument  is  a pointer to an interface index (see netdevice(7))
              in an integer.

       IPV6_MULTICAST_LOOP
              Control whether the socket sees multicast packets  that  it  has
              send itself.  Argument is a pointer to boolean.

       IPV6_PKTINFO
              Set  delivery  of  the  IPV6_PKTINFO control message on incoming
              datagrams.  Only allowed for  SOCK_DGRAM  or  SOCK_RAW  sockets.
              Argument is a pointer to a boolean value in an integer.

       IPV6_RTHDR,  IPV6_AUTHHDR,  IPV6_DSTOPS,  IPV6_HOPOPTS,  IPV6_FLOWINFO,
       IPV6_HOPLIMIT
              Set delivery of control messages for incoming datagrams contain-
              ing extension headers from the received packet.  IPV6_RTHDR  de-
              livers the routing header, IPV6_AUTHHDR delivers the authentica-
              tion header,  IPV6_DSTOPTS  delivers  the  destination  options,
              IPV6_HOPOPTS delivers the hop options, IPV6_FLOWINFO delivers an
              integer containing the flow ID, IPV6_HOPLIMIT delivers an  inte-
              ger  containing  the  hop count of the packet.  The control mes-
              sages have the same type as the socket option.  All these header
              options  can also be set for outgoing packets by putting the ap-
              propriate control message into the control buffer of sendmsg(2).
              Only  allowed for SOCK_DGRAM or SOCK_RAW sockets.  Argument is a
              pointer to a boolean value.

       IPV6_RECVERR
              Control receiving of asynchronous error options.  See IP_RECVERR
              in ip(7) for details.  Argument is a pointer to boolean.

       IPV6_ROUTER_ALERT
              Pass  forwarded packets containing a router alert hop-by-hop op-
              tion to this socket.  Only allowed for  SOCK_RAW  sockets.   The
              tapped packets are not forwarded by the kernel, it is the user's
              responsibility to send them out again.  Argument is a pointer to
              an  integer.  A positive integer indicates a router alert option
              value to intercept.  Packets carrying a router alert option with
              a  value  field containing this integer will be delivered to the
              socket.  A negative integer disables delivery  of  packets  with
              router alert options to this socket.

       IPV6_UNICAST_HOPS
              Set the unicast hop limit for the socket.  Argument is a pointer
              to an integer.  -1 in the value means  use  the  route  default,
              otherwise it should be between 0 and 255.

       IPV6_V6ONLY (since Linux 2.4.21 and 2.6)
              If  this  flag is set to true (non-zero), then the socket is re-
              stricted to sending and receiving IPv6 packets  only.   In  this
              case,  an IPv4 and an IPv6 application can bind to a single port
              at the same time.

              If this flag is set to false (zero), then the socket can be used
              to  send  and  receive packets to and from an IPv6 address or an
              IPv4-mapped IPv6 address.

              The argument is a pointer to a boolean value in an integer.

              The default value for this flag is defined by  the  contents  of
              the  file  /proc/sys/net/ipv6/bindv6only.  The default value for
              that file is 0 (false).

VERSIONS
       The older libinet6 libc5 based IPv6 API implementation for Linux is not
       described here and may vary in details.

       Linux  2.4  will  break  binary  compatibility for the sockaddr_in6 for
       64-bit hosts by changing the alignment of in6_addr and adding an  addi-
       tional sin6_scope_id field.  The kernel interfaces stay compatible, but
       a program including sockaddr_in6 or in6_addr into other structures  may
       not be.  This is not a problem for 32-bit hosts like i386.

       The  sin6_flowinfo  field  is  new  in  Linux 2.4.  It is transparently
       passed/read by the kernel when the passed address length  contains  it.
       Some programs that pass a longer address buffer and then check the out-
       going address length may break.

NOTES
       The sockaddr_in6 structure is bigger than the generic  sockaddr.   Pro-
       grams  that  assume  that  all  address types can be stored safely in a
       struct sockaddr need to be changed to use struct  sockaddr_storage  for
       that instead.

BUGS
       The  IPv6  extended  API as in RFC 2292 is currently only partly imple-
       mented; although the 2.2 kernel has near complete support for receiving
       options,  the  macros  for generating IPv6 options are missing in glibc
       2.1.

       IPSec support for EH and AH headers is missing.

       Flow label management is not complete and not documented here.

       This man page is not complete.

SEE ALSO
       cmsg(3), ip(7)

       RFC 2553: IPv6 BASIC API.  Linux tries to be compliant to this.

       RFC 2460: IPv6 specification.

COLOPHON
       This page is part of release 3.05 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux                             2008-07-17                           IPV6(7)

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