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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 routing table suggests	to route it to faith interface.	 In this case,
     the packet	will be	accepted by the	router,	regardless of list of IPv6 in-
     terface addresses assigned	to the router.	The packet will	be captured by
     an	IPv6 TCP socket, if it has IN6P_FAITH flag turned on and it has	match-
     ing address/port pairs.  In result, faith will let	you capture IPv6 TCP
     traffic to	some specific destination addresses.  Userland programs, such
     as	faithd(8) can use this behavior	to relay IPv6 TCP traffic to IPv4 TCP
     traffic.  The program can accept some specific IPv6 TCP traffic, perform
     getsockname(2) to get the IPv6 destination	address	specified by the
     client, and perform application-specific address mapping to relay IPv6
     TCP to IPv4 TCP.

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

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

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

     As	faith interface	implements potentially dangerous operation, great care
     must be taken when	configuring faith interface.  To avoid possible	mis-
     use, sysctl(8) variable net.inet6.ip6.keepfaith must be set to 1 prior to
     the use of	the interface.	When net.inet6.ip6.keepfaith is	0, no packet
     will be captured by faith interface.

     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 was first appeared in WIDE
     hydrangea IPv6 stack.

BSD				April 10, 1999				   BSD


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