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FAITH(4)		 BSD Kernel Interfaces Manual		      FAITH(4)

     faith -- IPv6-to-IPv4 TCP relay capturing interface

     device faith

     The faith interface captures IPv6 TCP traffic, for	implementing userland
     IPv6-to-IPv4 TCP relay like faithd(8).

     Each faith	interface is created at	runtime	using interface	cloning.  This
     is	most easily done with the ifconfig(8) create command or	using the
     cloned_interfaces variable	in rc.conf(5).

     Special action will be taken when IPv6 TCP	traffic	is seen	on a router,
     and the routing table suggests to route it	to the faith interface.	 In
     this case,	the packet will	be accepted by the router, regardless of the
     list of IPv6 interface addresses assigned to the router.  The packet will
     be	captured by an IPv6 TCP	socket,	if it has the IN6P_FAITH flag turned
     on	and matching address/port pairs.  As a result, faith will let you cap-
     ture IPv6 TCP traffic to some specific destination	addresses.  Userland
     programs, such as faithd(8) can use this behavior to relay	IPv6 TCP traf-
     fic to IPv4 TCP traffic.  The program can accept some specific IPv6 TCP
     traffic, perform getsockname(2) to	get the	IPv6 destination address spec-
     ified by the client, and perform application-specific address mapping to
     relay IPv6	TCP to IPv4 TCP.

     The IN6P_FAITH flag on a IPv6 TCP socket can be set by using
     setsockopt(2), with level IPPROTO_IPV6 and	optname	IPv6_FAITH.

     To	handle error reports by	ICMPv6,	some ICMPv6 packets routed to an faith
     interface will be delivered to IPv6 TCP, as well.

     To	understand how faith can be used, take a look at the source code of

     As	the faith interface implements potentially dangerous operations, great
     care must be taken	when configuring it.  To avoid possible	misuse,	the
     sysctl(8) variable	net.inet6.ip6.keepfaith	must be	set to 1 prior to us-
     ing the interface.	 When net.inet6.ip6.keepfaith is 0, no packets will be
     captured by the faith interface.

     The faith interface is intended to	be used	on routers, not	on hosts.

     inet(4), inet6(4),	faithd(8)

     Jun-ichiro	itojun Hagino and Kazu Yamamoto, An IPv6-to-IPv4 transport
     relay translator, RFC3142.

     The FAITH IPv6-to-IPv4 TCP	relay translator first appeared	in the WIDE
     hydrangea IPv6 stack.

BSD				April 10, 1999				   BSD


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