faith(4)

NAME

faith - IPv6-to-IPv4 TCP relay capturing interface

SYNOPSIS

device faith

DESCRIPTION

The faith interface captures IPv6 TCP traffic, for imple

menting 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 routing table suggests to route it to faith interface.

In this case,
the packet will be accepted by the router, regardless of

list of IPv6
interface addresses assigned to the router. The packet will

be captured
by an IPv6 TCP socket, if it has IN6P_FAITH flag turned on

and it has
matching address/port pairs. In result, faith will let you

capture IPv6
TCP traffic to some specific destination addresses. User

land 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 IPv6 TCP socket can be set by using

setsockopt(2),
with level equals to IPPROTO_IPV6 and optname equals to

IPv6_FAITH.

To handle error reports by ICMPv6, some of ICMPv6 packets

routed to faith
interface will be delivered to IPv6 TCP, as well.

To understand how faith can be used, take a look at source

code of
faithd(8).

As faith interface implements potentially dangerous opera

tion, great care
must be taken when configuring faith interface. To avoid

possible misuse, sysctl(8) variable net.inet6.ip6.keepfaith must be set

to 1 prior to
the use of the interface. When net.inet6.ip6.keepfaith is

0, no packet
will be captured by faith interface.

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 was first ap

peared in WIDE
hydrangea IPv6 stack.

BSD April 10, 1999

BSD