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           #include <sys/socket.h>
           #include <netinet/in.h>
           tcp6_socket = socket(AF_INET6, SOCK_STREAM, 0);
           raw6_socket = socket(AF_INET6, SOCK_RAW, protocol);
           udp6_socket = socket(AF_INET6, SOCK_DGRAM, protocol);


           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  IPv4  API  (see
           ip(7)).  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  byte
           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 to support this API  type
           to  support  both  protocols.   This  is  handled  transparently by the
           address handling functions in the C library.
           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 {
                   sa_family_t     sin6_family;   /* AF_INET6 */
                   in_port_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  depend-
           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.
                  Turn an AF_INET6 socket into a socket  of  a  different  address
                  family.   Only  AF_INET  is currently supported for that.  It is
                  allowed only 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.
                  Control membership in multicast groups.  Argument is  a  pointer
                  to a struct ipv6_mreq.
                  getsockopt(): Retrieve the current known path MTU of the current
                  socket.  Only valid when the socket has been connected.  Returns
                  an integer.
                  setsockopt(): Set the MTU to be used for the socket.  The MTU is
                  limited by the device MTU or the path MTU when path MTU  discov-
                  ery is enabled.  Argument is a pointer to integer.
                  Control  path-MTU  discovery on the socket.  See IP_MTU_DISCOVER
                  in ip(7) for details.
                  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.
                  Set the device for outgoing multicast  packets  on  the  socket.
                  This  is  allowed  only for SOCK_DGRAM and SOCK_RAW socket.  The
                  argument is a pointer to an interface index  (see  netdevice(7))
                  in an integer.
                  Control  whether  the  socket sees multicast packets that it has
                  send itself.  Argument is a pointer to boolean.
           IPV6_RECVPKTINFO (since Linux 2.6.14)
                  Set delivery of the IPV6_PKTINFO  control  message  on  incoming
                  datagrams.   Such control messages contain a struct in6_pktinfo,
                  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.
                  Control receiving of asynchronous error options.  See IP_RECVERR
                  in ip(7) for details.  Argument is a pointer to boolean.
                  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.
                  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 (nonzero), 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).


           ENODEV The user tried to bind(2) to a link-local IPv6 address, but  the
                  sin6_scope_id  in  the  supplied sockaddr_in6 structure is not a
                  valid interface index.


           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


           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
           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.


           cmsg(3), ip(7)
           RFC 2553: IPv6  BASIC  API;  Linux  tries  to  be  compliant  to  this.
           RFC 2460: IPv6 specification.

    Linux 2012-12-16 IPV6(7)


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