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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 default routing table suggests to route it	to the faith inter-
     face.  In this case, the packet will be accepted by the router, regard-
     less 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 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 ad-
     dress specified 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			       January 23, 2012				   BSD


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