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NetBSD 6.1.5 - man page for inet6 (netbsd section 4)

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INET6(4)			   BSD Kernel Interfaces Manual 			 INET6(4)

NAME
     inet6 -- Internet protocol version 6 family

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

DESCRIPTION
     The inet6 family is an updated version of 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 Protocol version 6 (IPv6)
     transport layer, and using the IPv6 address format.  The inet6 family provides protocol sup-
     port for the SOCK_STREAM, SOCK_DGRAM, and SOCK_RAW socket types; the SOCK_RAW interface pro-
     vides access to the IPv6 protocol.

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

     Sockets bound to the inet6 family use the following addressing structure:

	   struct sockaddr_in6 {
		   uint8_t	   sin6_len;
		   sa_family_t	   sin6_family;
		   in_port_t	   sin6_port;
		   uint32_t	   sin6_flowinfo;
		   struct in6_addr sin6_addr;
		   uint32_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 messages.

     The IPv6 specification defines scoped addresses, like link-local or site-local addresses.	A
     scoped address is ambiguous to the kernel, if it is specified without a scope identifier.
     To manipulate scoped addresses properly from the userland, programs must use the advanced
     API defined in RFC 2292.  A compact description of the advanced API is available in ip6(4).
     If a scoped address is specified without an 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.

     The KAME implementation supports an extended numeric IPv6 address notation for link-local
     addresses, like ``fe80::1%de0'' to specify ``fe80::1 on de0 interface''.  This notation is
     supported by getaddrinfo(3) and getnameinfo(3).  Some of normal userland programs, such as
     telnet(1) or ftp(1), are able to use this notation.  With special programs like ping6(8),
     you can specify the outgoing interface by an extra command line option to disambiguate
     scoped addresses.

     Scoped addresses are handled specially in the kernel.  In kernel structures like routing
     tables or interface structures, a scoped address will have its interface index embedded into
     the address.  Therefore, the address in some kernel structures is not the same as that on
     the wire.	The embedded index will become visible through a PF_ROUTE socket, kernel memory
     accesses via kvm(3) and on some other occasions.  HOWEVER, users should never use the embed-
     ded form.	For details please consult
     http://www.kame.net/dev/cvsweb.cgi/kame/IMPLEMENTATION.  Note that the above URL describes
     the situation with the latest KAME tree, not the NetBSD tree.

PROTOCOLS
     The inet6 family comprises the IPv6 network protocol, Internet Control Message Protocol ver-
     sion 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 pro-
     tocol is accessible from a raw socket.

   Interaction between IPv4/v6 sockets
     By default, NetBSD does not route IPv4 traffic to AF_INET6 sockets.  The default behavior
     intentionally violates RFC 2553 for security reasons.  Listen to two sockets if you want to
     accept both IPv4 and IPv6 traffic.  IPv4 traffic may be routed with certain per-socket/per-
     node configuration, however, it is not recommended to do so.  Consult ip6(4) for details.

     The behavior of AF_INET6 TCP/UDP socket is documented in RFC 2553.  Basically, it says this:
     o	 A specific bind on an AF_INET6 socket (bind(2) with an address specified) should accept
	 IPv6 traffic to that address only.
     o	 If you perform a wildcard bind 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 an IPv6 address like ::ffff:10.1.1.1.	This is called an IPv4 mapped
	 address.
     o	 If there are both a wildcard bind AF_INET socket and a wildcard bind AF_INET6 socket on
	 one TCP/UDP port, they should behave separately.  IPv4 traffic should be routed to the
	 AF_INET socket and IPv6 should be routed to the AF_INET6 socket.

     However, RFC 2553 does not define the ordering constraint between calls to 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 sock-
     ets.  It is recommended to listen to two sockets, one for AF_INET and another for AF_INET6,
     when you would like to accept both IPv4 and IPv6 traffic.

     It should also be noted that malicious parties can take advantage of the complexity pre-
     sented above, and are able to bypass access control, if the target node routes IPv4 traffic
     to AF_INET6 socket.  Users are advised to take care handling connections from IPv4 mapped
     address to AF_INET6 sockets.

SEE ALSO
     ioctl(2), socket(2), sysctl(3), icmp6(4), intro(4), ip6(4), tcp(4), udp(4)

     Qing Li, Tatuya Jinmei, and Keiichi Shima, IPv6 Core Protocols Implementation, Morgan
     Kaufmann, 2006.

     Qing Li, Tatuya Jinmei, and Keiichi Shima, IPv6 Advanced Protocols Implementation, Morgan
     Kaufmann, 2007.

STANDARDS
     Tatuya 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
     The inet6 protocol interfaces are defined in RFC 2553 and RFC 2292.  The implementation
     described herein appeared in the WIDE/KAME project.

BUGS
     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.

     Users are suggested to implement ``version independent'' code as much as possible, as you
     will need to support both inet(4) and inet6.

BSD					  March 10, 2010				      BSD
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