NAME
faith —
IPv6-to-IPv4 TCP relay capturing
interface
SYNOPSIS
pseudo-device faith
[count]
DESCRIPTION
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 ifconfig
faithN create command
or by setting up a
hostname.if(5) configuration file for
netstart(8).
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
captured IPv6 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 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 an IPv6 TCP socket
can be set by using
setsockopt(2), with level set to
IPPROTO_IPV6 and optname set to
IPv6_FAITH.
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
faithd(8).
As the faith interface implements a
potentially dangerous operation, 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 on hosts.
SEE ALSO
STANDARDS
J. Hagino and K. Yamamoto, An IPv6-to-IPv4 transport relay translator, RFC 3142, June 2001.
HISTORY
The FAITH IPv6-to-IPv4 TCP relay translator first appeared in WIDE hydrangea IPv6 stack.