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NAME    [Toc]    [Back]

       ipv6, PF_INET6 - Linux IPv6 protocol implementation

SYNOPSIS    [Toc]    [Back]

       #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    [Toc]    [Back]

       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-mappedon-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 connection
 or packet to a IPv6 socket its source address will be mapped to v6
       and it'll be mapped to v6.

ADDRESS FORMAT    [Toc]    [Back]

	      struct sockaddr_in6 {
		  u_int16_t	  sin6_family;/* AF_INET6 */
		  u_int16_t	  sin6_port;/* port number */
		  u_int32_t	  sin6_flowinfo;/* IPv6 flow information */
		  struct in6_addr sin6_addr;/* IPv6 address */
		  u_int32_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  128bit  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 numbers,
 separated with a ':'. '::' stands for a string of 0  bits.   Special
  addresses	are  ::1  for  loopback  and  FFFF::<IPv4 address> for

       The port space of IPv6 is shared with IPv4.

SOCKET OPTIONS    [Toc]    [Back]

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

       IPV6_MULTICAST_HOPS    [Toc]    [Back]
	      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    [Toc]    [Back]
	      Set  the	device	for  outgoing multicast packets on the socket.
	      This is only allowed for SOCK_DGRAM and  SOCK_RAW  socket.   The
	      argument	is an pointer to an interface index (see netdevice(7))
	      in an integer.

       IPV6_ADDRFORM    [Toc]    [Back]
	      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 a integer
	      containing AF_INET.  This is useful to pass v4-mapped sockets as
	      filedescriptors to programs that don't know how to deal with the
	      IPv6 API.

       IPV6_PKTINFO    [Toc]    [Back]
	      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.

	      Set delivery of control messages for incoming datagrams containing
  extension headers from the received packet.	IPV6_RTHDR delivers
 the routing header, IPV6_AUTHHDR delivers the authentication
  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 integer
 containing the hop count of the packet.   The  control  messages
  have the same type as the socket option. All these header
	      options can also be set for outgoing packets by putting the  appropriate
 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_MULTICAST_LOOP    [Toc]    [Back]
	      Control  whether	the  socket sees multicast packets that is has
	      send itself.  Argument is a pointer to boolean.

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

       IPV6_MTU    [Toc]    [Back]
	      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    [Toc]    [Back]
	      Control path mtu discovery on the socket. See IP_MTU_DISCOVER in
	      ip(7) for details.

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

       IPV6_ROUTER_ALERT    [Toc]    [Back]
	      Pass  all forwarded packets containing an router alert option to
	      this socket.  Only allowed for datagram sockets  and  for  root.
	      Argument is a pointer to boolean.

VERSIONS    [Toc]    [Back]

       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
       64bit  hosts  by changing the alignment of in6_addr and adding an additional
 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 32bit 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 outgoing
 address length may break.

PORTING NOTES    [Toc]    [Back]

       The  sockaddr_in6  structure is bigger than the generic sockaddr.  Programs
 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    [Toc]    [Back]

       The IPv6 extended API as in RFC2292 is currently only partly implemented;
 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    [Toc]    [Back]

       ip(7), cmsg(3)

       RFC2553: IPv6 BASIC API. Linux tries to be compliant to this.

       RFC2460: IPv6 specification.

Linux Man Page			  1999-06-29			       IPV6(7)
[ Back ]
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