NAME
faith —
IPv6-to-IPv4 TCP relay
capturing interface
SYNOPSIS
pseudo-device faith
DESCRIPTION
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
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, RFC 3142,
ftp://ftp.isi.edu/in-notes/rfc3142.txt,
June 2001.
HISTORY
The FAITH IPv6-to-IPv4 TCP relay translator first appeared in the WIDE hydrangea
IPv6 stack.