| FAITH(4) | Device Drivers Manual | FAITH(4) | 
faith —
pseudo-device faith
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
    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.
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 2001.
| January 9, 2010 | NetBSD 9.4 |