NAME¶
faith —
IPv6-to-IPv4 TCP relay
capturing interface
SYNOPSIS¶
device faith
DESCRIPTION¶
The
faith interface captures IPv6 TCP traffic, for
implementing 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 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.
The
IN6P_FAITH
flag on a 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, RFC3142.
HISTORY¶
The FAITH IPv6-to-IPv4 TCP relay translator first appeared in the WIDE hydrangea
IPv6 stack.