faith - IPv6-to-IPv4 TCP relay capturing interface
pseudo-device faith [count]
The faith interface captures IPv6 TCP traffic, for implementing userland
IPv6-to-IPv4 TCP relay similar to faithd(8).
A faith interface can be created at runtime using the
create command or by setting up a hostname.if(5) configuration file for
Special action will be taken when IPv6 TCP traffic is seen
on a router,
and the routing table suggests routing 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 is
captured by an IPv6 TCP socket, if it has the IN6P_FAITH
flag turned on
and it has matching address/port pairs. Thus, faith allows
TCP traffic to be relayed 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
TCP traffic, perform getsockname(2) to get the IPv6 destination address
specified by the client, and perform application-specific
to relay IPv6 TCP to IPv4 TCP.
The IN6P_FAITH flag on an IPv6 TCP socket can be set by using
setsockopt(2), with level set to IPPROTO_IPV6 and optname
To handle error reports by ICMPv6, some of the ICMPv6 packets routed to
the 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 a potentially dangerous
great care must be taken when configuring the faith interface. To avoid
possible misuse, the sysctl(8) variable net.inet6.ip6.keepfaith must be
set to 1 prior to use of the interface. When net.inet6.ip6.keepfaith is
0, no packet is captured by the faith interface.
The faith interface is intended to be used on routers, not
inet(4), inet6(4), hostname.if(5), faithd(8), netstart(8)
Jun-ichiro itojun Hagino and Kazu Yamamoto, "An IPv6-to-IPv4
relay translator", RFC 3142, June 2001,
The FAITH IPv6-to-IPv4 TCP relay translator first appeared
hydrangea IPv6 stack.
OpenBSD 3.6 April 10, 1999
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