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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 Protocol 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 byteorder.  The include
     file <netinet/in.h> defines this address as a discriminated union.

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

	   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 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 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 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 IMPLEMENTATION supplied with KAME kit.

     The inet6 family is comprised of the IPv6 network protocol, Internet Control Message Proto-
     col 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 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 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 forwarding 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 applies 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 accept.  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 possible DoS attacks.

     IPV6CTL_ACCEPT_RTADV    (ip6.accept_rtadv) Boolean: enable/disable receiving of ICMPv6
			     router advertisement packets, and autoconfiguration of address pre-
			     fixes and default routers.  The node must be a host (not a router)
			     for the option to be meaningful.  Defaults 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 between IPv6 packet
			     forwarding engine log output (in seconds).

     IPV6CTL_HDRNESTLIMIT    (ip6.hdrnestlimit) Integer: default number of the maximum IPv6
			     extension headers permitted on incoming 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 automatic filling of
			     IPv6 flowlabel field, for outstanding connected transport protocol
			     packets.  The field might be used by intermediate routers to iden-
			     tify packet flows.  Defaults to on.

     IPV6CTL_DEFMCASTHLIM    (ip6.defmcasthlim) Integer: default hop limit value for an IPv6 mul-
			     ticast 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) tunnel 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 renum-
			     bering prefix babysitting, in seconds.

     IPV6CTL_MAPPED_ADDR     (ip6.mapped_addr) Boolean: enable/disable use of IPv4 mapped address
			     on AF_INET6 sockets.  Defaults to on.

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

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

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

   Interaction between IPv4/v6 sockets
     The behavior of AF_INET6 TCP/UDP socket is documented in RFC2553.	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:	This is called an IPv4 mapped
     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).	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.

     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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