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RedHat 9 (Linux i386) - man page for ipv6 (redhat section 7)

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

ADDRESS FORMAT
	      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 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_UNICAST_HOPS
	      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
	      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 an pointer to an interface
	      index (see netdevice(7)) in an integer.

       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 con-
	      nected and bound to a v4-mapped-on-v6 address. The argument is a pointer to a inte-
	      ger  containing  AF_INET.  This is useful to pass v4-mapped sockets as filedescrip-
	      tors to programs that don't know how to deal with the IPv6 API.

       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 containing extension  head-
	      ers 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 con-
	      trol 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
	      Control whether the socket sees multicast packets that is has send  itself.   Argu-
	      ment is a pointer to boolean.

       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_RECVERR
	      Control  receiving  of  asynchronous error options. See IP_RECVERR in ip(7) for de-
	      tails.  Argument is a pointer to boolean.

       IPV6_ROUTER_ALERT
	      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
       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 inter-
       faces stay compatible, but a program including sockaddr_in6 or in6_addr into other  struc-
       tures 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  buf-
       fer and then check the outgoing address length may break.

PORTING NOTES
       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
       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 op-
       tions 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
       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)


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