.\"	$OpenBSD: faithd.8,v 1.24 2003/04/14 06:51:49 jmc Exp $
.\"	$KAME: faithd.8,v 1.36 2002/05/09 13:59:16 itojun Exp $
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.Dd May 17, 1998
.Dt FAITHD 8
.Os
.Sh NAME
.Nm faithd
.Nd FAITH IPv6/v4 translator daemon
.Sh SYNOPSIS
.Nm
.Op Fl dp
.Op Fl f Ar configfile
.Ar service
.Op Ar serverpath Op Ar serverargs
.\".Nm ""
.Sh DESCRIPTION
.Nm
provides an IPv6-to-IPv4 TCP relay.
.Nm
must be used on an IPv4/v6 dual stack router.
.Pp
When
.Nm
receives
.Tn TCPv6
traffic,
.Nm
will relay the
.Tn TCPv6
traffic to
.Tn TCPv4 .
The destination for the relayed
.Tn TCPv4
connection is determined by the last 4 octets of the original
.Tn IPv6
destination.
For example, if
.Li 3ffe:0501:4819:ffff::
is reserved for
.Nm Ns ,
and the
.Tn TCPv6
destination address is
.Li 3ffe:0501:4819:ffff::0a01:0101 ,
the traffic is relayed to IPv4 destination
.Li 10.1.1.1 .
.Pp
To use the
.Nm
translation service,
an IPv6 address prefix must be reserved for mapping IPv4 addresses onto.
The kernel must be properly configured to route all the TCP connections
toward the reserved IPv6 address prefix into the
.Xr faith 4
pseudo interface, by using the
.Xr route 8
command.
Also,
.Xr sysctl 8
should be used to configure
.Dv net.inet6.ip6.keepfaith
to
.Dv 1 .
.Pp
The router must be configured to capture all the TCP traffic
for a given reserved
.Tn IPv6
address prefix, by using the
.Xr route 8
and
.Xr sysctl 8
commands.
.Pp
.Nm
needs a special name-to-address translation logic, so that
hostnames get resolved into a special
.Tn IPv6
address prefix.
For small-scale installation, use
.Xr hosts 5 .
For large-scale installation, it is useful to have
a DNS server with special address translation support.
An implementation called
.Nm totd
is available
at
.Pa http://www.vermicelli.pasta.cs.uit.no/ipv6/software.html .
Make sure you do not propagate translated DNS records to normal DNS cloud,
it is highly harmful.
.\".Ss Daemon mode
When
.Nm
.\"is invoked as a stand-alone program,
is invoked,
.Nm
will daemonize itself.
.Nm
will listen to
.Tn TCPv6
port
.Ar service .
If
.Tn TCPv6
traffic to port
.Ar service
is found, it relays the connection.
.Pp
Since
.Nm
listens to TCP port
.Ar service ,
it is not possible to run local TCP daemons for port
.Ar service
on the router, using
.Xr inetd 8
or other standard mechanisms.
Local daemons can be run on the router
by specifying a
.Ar serverpath
to
.Nm Ns .
.Nm
will invoke a local daemon at
.Ar serverpath
if the destination address is a local interface address,
and will perform translation to IPv4 TCP in other cases.
.Ar Serverargs
can also be specified as
arguments for the local daemon.
.Pp
The following options are available:
.Bl -tag -width indent
.It Fl d
Debugging information will be generated using
.Xr syslog 3 .
.It Fl f Ar configfile
Specify a configuration file for access control.
See below.
.It Fl p
Use the privileged TCP port number as a source port,
for an IPv4 TCP connection toward the final destination.
For relaying
.Xr ftp 1
this flag is not necessary as special program code is supplied.
.El
.Pp
.Nm
will relay both normal and out-of-band TCP data.
It is capable of emulating TCP half close as well.
.Nm
includes special support for protocols used by
.Xr ftp 1 .
When translating FTP protocol,
.Nm
translates network level addresses in
.Li PORT/LPRT/EPRT
and
.Li PASV/LPSV/EPSV
commands.
.Pp
Inactive sessions will be disconnected in 30 minutes,
to avoid stale sessions from chewing up resources.
This may be inappropriate for some of the services
.Pq should this be configurable? .
.Ss Access control
To prevent malicious access,
.Nm
implements a simple address-based access control.
With
.Pa /etc/faithd.conf
.Po
or
.Ar configfile
specified by
.Fl f
.Pc ,
.Nm
will avoid relaying unwanted traffic.
.Pa faithd.conf
contains directives with the following format:
.Bl -bullet
.It
.Xo
.Ic Ar src/slen Li deny Ar dst/dlen
.Xc
.Pp
If the source address of a query matches
.Ar src/slen ,
and the translated destination address matches
.Ar dst/dlen ,
deny the connection.
.It
.Xo
.Ic Ar src/slen Li permit Ar dst/dlen
.Xc
.Pp
If the source address of a query matches
.Ar src/slen ,
and the translated destination address matches
.Ar dst/dlen ,
permit the connection.
.El
.Pp
The directives are evaluated in sequence,
and the first matching entry will be effective.
If there is no match
.Pq the end of the ruleset has been reached ,
the traffic is denied.
.\".Pp
.\"With inetd mode,
.\"traffic may be filtered by using access control functionality in
.\".Xr inetd 8 .
.Sh RETURN VALUES
.Nm
exits with
.Dv EXIT_SUCCESS
.Pq 0
on success, and
.Dv EXIT_FAILURE
.Pq 1
on error.
.Sh EXAMPLES
Before invoking
.Nm Ns ,
the
.Xr faith 4
interface has to be configured properly:
.Bd -literal -offset
# sysctl -w net.inet6.ip6.accept_rtadv=0
# sysctl -w net.inet6.ip6.forwarding=1
# sysctl -w net.inet6.ip6.keepfaith=1
# ifconfig faith0 up
# route add -inet6 3ffe:501:4819:ffff:: -prefixlen 96 ::1
# route change -inet6 3ffe:501:4819:ffff:: -prefixlen 96 -ifp faith0
.Ed
.\".Ss Daemon mode samples
.Pp
To translate
.Li telnet
service, and provide no local telnet service, invoke
.Nm
as follows:
.Bd -literal -offset
# faithd telnet
.Ed
.Pp
Provide local telnet service via
.Xr telnetd 8
using
.Pa /usr/libexec/telnetd .
.Bd -literal -offset
# faithd telnet /usr/libexec/telnetd telnetd
.Ed
.Pp
Pass extra arguments to the local daemon:
.Bd -literal -offset
# faithd ftp /usr/libexec/ftpd ftpd -l
.Ed
.Pp
Here are some other examples.
If the service checks the source port range,
.Fl p
may be required.
.Bd -literal -offset
# faithd ssh
# faithd telnet /usr/libexec/telnetd telnetd
.Ed
.Ss Access control samples
The following illustrates a simple
.Pa faithd.conf
setting.
.Bd -literal -offset
# permit anyone from 3ffe:501:ffff::/48 to use the translator,
# to connect to the following IPv4 destinations:
# - any location except 10.0.0.0/8 and 127.0.0.0/8.
# Permit no other connections.
#
3ffe:501:ffff::/48 deny 10.0.0.0/8
3ffe:501:ffff::/48 deny 127.0.0.0/8
3ffe:501:ffff::/48 permit 0.0.0.0/0
.Ed
.Sh SEE ALSO
.Xr faith 4 ,
.Xr route 8 ,
.Xr sysctl 8
.Rs
.%A Jun-ichiro itojun Hagino
.%A Kazu Yamamoto
.%T "An IPv6-to-IPv4 transport relay translator"
.%B RFC3142
.%O ftp://ftp.isi.edu/in-notes/rfc3142.txt
.%D June 2001
.Re
.\"
.Sh HISTORY
The
.Nm
command first appeared in WIDE Hydrangea IPv6 protocol stack kit.
.\"
.Sh SECURITY CONSIDERATIONS
It is very insecure to use IP-address based authentication, for connections relayed by
.Nm Ns ,
and any other TCP relaying services.
.Pp
Administrators are advised to limit accesses to
.Nm
using
.Pa faithd.conf ,
or by using IPv6 packet filters,
to protect the
.Nm
service from malicious parties and avoid theft of service/bandwidth.
IPv6 destination addresses can be limited by
carefully configuring routing entries that point to
.Xr faith 4 ,
using
.Xr route 8 .
IPv6 source addresses need to be filtered  using a packet filter.
Documents listed in
.Sx SEE ALSO
have more discussions on this topic.