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FAITH(4)                     Device Drivers Manual                    FAITH(4)

     faith - IPv6-to-IPv4 TCP relay capturing interface

     pseudo-device faith

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

     faith interfaces are dynamically created and destroyed with the
     ifconfig(8) create and destroy subcommands.

     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
     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.

     IN6P_FAITH flag on an 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
     using 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", RFC 3142, ftp://ftp.isi.edu/in-notes/rfc3142.txt, June

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

NetBSD 10.99                    January 9, 2010                   NetBSD 10.99