NAME

       faith — IPv6-to-IPv4 TCP relay capturing interface

SYNOPSIS

       device faith

DESCRIPTION

       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 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.

       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 faithd(8).

       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.

SEE ALSO

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

       Jun-ichiro itojun Hagino and Kazu Yamamoto, An IPv6-to-IPv4 transport relay translator, RFC3142.

HISTORY

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

Debian                                          January 23, 2012                                        FAITH(4)