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

NAME
     ffaaiitthh - IPv6-to-IPv4 TCP relay capturing interface

SYNOPSIS
     ppsseeuuddoo-ddeevviiccee ffaaiitthh [count]

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

     Special action will be taken when IPv6 TCP traffic is seen on a router,
     and routing table suggests to route it to ffaaiitthh 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 IN6PFAITH flag turned on and it has
     matching address/port pairs.  In result, ffaaiitthh 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 IN6PFAITH flag on IPv6 TCP socket can be set by using setsockopt(2),
     with level equals to IPPROTOIPV6 and optname equals to IPv6FAITH.

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

     To understand how ffaaiitthh can be used, take a look at source code of
     faithd(8).

     As ffaaiitthh interface implements potentially dangerous operation, great care
     must be taken when configuring ffaaiitthh 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 ffaaiitthh interface.

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

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

     Jun-ichiro itojun Hagino and Kazu Yamamoto, An IPv6-to-IPv4 transport
     relay translator, internet draft, draft-ietf-ngtrans-tcpudp-relay-04.txt,
     work in progress material.

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

BSD                             April 10, 1999                             BSD