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FAITH(4)	       FreeBSD 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
     interface 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
     matching 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, per-
     form 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.

FreeBSD	11.1			April 10, 1999			  FreeBSD 11.1


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