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NAME    [Toc]    [Back]

     inet6 -- Internet protocol version 6 family

SYNOPSIS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

     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.

ADDRESSING    [Toc]    [Back]

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

     Sockets bound to the inet6 family utilize 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 affect ``wildcard'' matching on incoming

     The IPv6 specification defines scoped addresses, like link-local or sitelocal
 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 embedded form.  For details please consult
     IMPLEMENTATION supplied with KAME kit.

PROTOCOLS    [Toc]    [Back]

     The inet6 family is comprised of the IPv6 network protocol, Internet Control
 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
     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    [Toc]    [Back]
     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 prefixes 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 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) tunnel

     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 prohibited
 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 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
     By default, FreeBSD does not route IPv4 traffic to AF_INET6 sockets.  The
     default behavior intentionally violates RFC2553 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

     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 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).  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
     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 sockets.

SEE ALSO    [Toc]    [Back]

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

STANDARDS    [Toc]    [Back]

     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.

HISTORY    [Toc]    [Back]

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

BUGS    [Toc]    [Back]

     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.

FreeBSD 5.2.1		       January 29, 1999 		 FreeBSD 5.2.1
[ Back ]
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