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

     inet6 -- Internet protocol	version	6 family

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

     The inet6 family is an updated version of inet(4) family.	While inet(4)
     implements	Internet Protocol version 4, inet6 implements Internet Proto-
     col version 6.

     inet6 is a	collection of protocols	layered	atop the Internet Protocol
     version 6 (IPv6) transport	layer, and utilizing the IPv6 address format.
     The inet6 family provides protocol	support	for the	SOCK_STREAM,
     SOCK_DGRAM, and SOCK_RAW socket types; the	SOCK_RAW interface provides
     access to the IPv6	protocol.

     IPv6 addresses are	16 byte	quantities, stored in network standard byte-
     order.  The include file <netinet/in.h> defines this address as a dis-
     criminated	union.

     Sockets bound to the inet6	family utilize the following addressing	struc-

	   struct sockaddr_in6 {
		   u_int8_t	   sin6_len;
		   u_int8_t	   sin6_family;
		   u_int16_t	   sin6_port;
		   u_int32_t	   sin6_flowinfo;
		   struct in6_addr sin6_addr;
		   u_int32_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 affect "wildcard"	matching on incoming

     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
     RFC2292.  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 nota-
     tion 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 struc-
     tures like	routing	tables or interface structures,	a scoped address will
     have its interface	index embedded into the	address.  Therefore, the ad-
     dress 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 mem-
     ory accesses via kvm(3) and on some other occasions.  HOWEVER, users
     should never use the embedded form.  For details please consult
     IMPLEMENTATION supplied with KAME kit.

     The inet6 family is comprised of the IPv6 network protocol, Internet Con-
     trol Message Protocol version 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 ab-
     straction.	 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 protocol is accessible from a raw socket.

   MIB Variables
     A number of variables are implemented in the net.inet6 branch of the
     sysctl(3) MIB.  In	addition to the	variables supported by the transport
     protocols (for which the respective manual	pages may be consulted), the
     following general variables are defined:

     IPV6CTL_FORWARDING	     (ip6.forwarding) Boolean: enable/disable forward-
			     ing of IPv6 packets.  Also, identify if the node
			     is	acting as a router.  Defaults to off.

     IPV6CTL_SENDREDIRECTS   (ip6.redirect) Boolean: enable/disable sending of
			     ICMPv6 redirects in response to unforwardable
			     IPv6 packets.  This option	is ignored unless the
			     node is routing IPv6 packets, and should normally
			     be	enabled	on all systems.	 Defaults to on.

     IPV6CTL_DEFHLIM	     (ip6.hlim)	Integer: default hop limit value to
			     use for outgoing IPv6 packets.  This value	ap-
			     plies to all the transport	protocols on top of
			     IPv6.  There are APIs to override the value.

     IPV6CTL_MAXFRAGPACKETS  (ip6.maxfragpackets) Integer: default maximum
			     number of fragmented packets the node will	ac-
			     cept.  0 means that the node will not accept any
			     fragmented	packets.  -1 means that	the node will
			     accept as many fragmented packets as it receives.
			     The flag is provided basically for	avoiding pos-
			     sible DoS attacks.

     IPV6CTL_ACCEPT_RTADV    (ip6.accept_rtadv)	Boolean: enable/disable	re-
			     ceiving of	ICMPv6 router advertisement packets,
			     and autoconfiguration of address prefixes and de-
			     fault routers.  The node must be a	host (not a
			     router) for the option to be meaningful.  De-
			     faults to off.

     IPV6CTL_KEEPFAITH	     (ip6.keepfaith) Boolean: enable/disable "FAITH"
			     TCP relay IPv6-to-IPv4 translator code in the
			     kernel.  Refer faith(4) and faithd(8) for detail.
			     Defaults to off.

     IPV6CTL_LOG_INTERVAL    (ip6.log_interval)	Integer: default interval be-
			     tween IPv6	packet forwarding engine log output
			     (in seconds).

     IPV6CTL_HDRNESTLIMIT    (ip6.hdrnestlimit)	Integer: default number	of the
			     maximum IPv6 extension headers permitted on in-
			     coming IPv6 packets.  If set to 0,	the node will
			     accept as many extension headers as possible.

     IPV6CTL_DAD_COUNT	     (ip6.dad_count) Integer: default number of	IPv6
			     DAD (duplicated address detection)	probe packets.
			     The packets will be generated when	IPv6 interface
			     addresses are configured.

     IPV6CTL_AUTO_FLOWLABEL  (ip6.auto_flowlabel) Boolean: enable/disable au-
			     tomatic filling of	IPv6 flowlabel field, for out-
			     standing connected	transport protocol packets.
			     The field might be	used by	intermediate routers
			     to	identify packet	flows.	Defaults to on.

     IPV6CTL_DEFMCASTHLIM    (ip6.defmcasthlim)	Integer: default hop limit
			     value for an IPv6 multicast packet	sourced	by the
			     node.  This value applies to all the transport
			     protocols on top of IPv6.	There are APIs to
			     override the value	as documented in ip6(4).

     IPV6CTL_GIF_HLIM	     (ip6.gifhlim) Integer: default maximum hop	limit
			     value for an IPv6 packet generated	by gif(4) tun-
			     nel interface.

     IPV6CTL_KAME_VERSION    (ip6.kame_version)	String:	identifies the version
			     of	KAME IPv6 stack	implemented in the kernel.

     IPV6CTL_USE_DEPRECATED  (ip6.use_deprecated) Boolean: enable/disable use
			     of	deprecated address, specified in RFC2462
			     5.5.4.  Defaults to on.

     IPV6CTL_RR_PRUNE	     (ip6.rr_prune) Integer: default interval between
			     IPv6 router renumbering prefix babysitting, in

     IPV6CTL_V6ONLY	     (ip6.v6only) Boolean: enable/disable the prohib-
			     ited use of IPv4 mapped address on	AF_INET6 sock-
			     ets.  Defaults to off.

     IPV6CTL_RTEXPIRE	     (ip6.rtexpire) Integer: lifetime in seconds of
			     protocol-cloned IP	routes after the last refer-
			     ence drops	(default one hour).

     IPV6CTL_RTMINEXPIRE     (ip6.rtminexpire) Integer:	minimum	value of
			     ip.rtexpire (default ten seconds).

     IPV6CTL_RTMAXCACHE	     (ip6.rtmaxcache) Integer: trigger level of
			     cached, unreferenced, protocol-cloned routes
			     which initiates dynamic adaptation	(default 128).

   Interaction between IPv4/v6 sockets
     The behavior of AF_INET6 TCP/UDP socket is	documented in RFC2553.	Basi-
     cally, it says this:
     o	 A specific bind on an AF_INET6	socket (bind(2)	with an	address	speci-
	 fied) 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:  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, RFC2553 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).  Imple-
     mented behavior is	very different from kernel to kernel.  Therefore, it
     is	unwise to rely too much	upon the behavior of AF_INET6 wildcard bind
     sockets.  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

     It	should also be noted that malicious parties can	take advantage of the
     complexity	presented 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 sock-

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

     Tatsuya 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.

     The inet6 protocol	interfaces are defined in RFC2553 and RFC2292.	The
     implementation described herein appeared in the WIDE/KAME project.

     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			       January 29, 1999				   BSD


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