freebsd-dev/usr.sbin/faithd/faithd.8

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.Dd August 2, 2011
.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
.Sh DESCRIPTION
The
.Nm
utility provides IPv6-to-IPv4 TCP relaying.
It can only be used on an IPv4/v6 dual stack router.
.Pp
When
.Nm
receives
.Tn TCPv6
traffic, it will relay the
.Tn TCPv6
traffic to
.Tn TCPv4 .
The destination for the relayed
.Tn TCPv4
connection will be determined by the last 4 octets of the original
.Tn IPv6
destination.
For example, if
.Li 3ffe:0501:4819:ffff::
is reserved for
.Nm ,
and the
.Tn TCPv6
destination address is
.Li 3ffe:0501:4819:ffff::0a01:0101 ,
the traffic will be 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 into.
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, 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 the reserved
.Tn IPv6
address prefix, by using
.Xr route 8
and
.Xr sysctl 8
commands.
.Pp
The
.Nm
utility needs special name-to-address translation logic, so that
hostnames get resolved into the special
.Tn IPv6
address prefix.
For small-scale installations, use
.Xr hosts 5 ;
For large-scale installations, 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/software/totd.html .
Make sure you do not propagate translated DNS records over to normal
DNS, as it can cause severe problems.
.Ss Daemon mode
When
.Nm
is invoked as a standalone program,
.Nm
will daemonize itself.
The
.Nm
utility 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.
By specifying
.Ar serverpath
to
.Nm ,
you can run local daemons on the router.
The
.Nm
utility 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.
You can also specify
.Ar serverargs
for the 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 privileged TCP port number as source port,
for IPv4 TCP connection toward final destination.
For relaying
.Xr ftp 1 ,
this flag is not necessary as special program code is supplied.
.El
.Pp
The
.Nm
utility will relay both normal and out-of-band TCP data.
It is capable of emulating TCP half close as well.
The
.Nm
utility includes special support for protocols used by
.Xr ftp 1 .
When translating the 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 prevent stale sessions from chewing up resources.
This may be inappropriate for some services
(should this be configurable?).
.Ss inetd mode
When
.Nm
is invoked via
.Xr inetd 8 ,
.Nm
will handle connections passed from standard input.
If the connection endpoint is in the reserved IPv6 address prefix,
.Nm
will relay the connection.
Otherwise,
.Nm
will invoke a service-specific daemon like
.Xr telnetd 8 ,
by using the command argument passed from
.Xr inetd 8 .
.Pp
The
.Nm
utility determines operation mode by the local TCP port number,
and enables special protocol handling whenever necessary/possible.
For example, if
.Nm
is invoked via
.Xr inetd 8
on the FTP port, it will operate as an FTP relay.
.Pp
The operation mode requires special support for
.Nm
in
.Xr inetd 8 .
.Ss Access control
To prevent malicious access,
.Nm
implements simple address-based access control.
With
.Pa /etc/faithd.conf
(or
.Ar configfile
specified by
.Fl f ) ,
.Nm
will avoid relaying unwanted traffic.
The
.Pa faithd.conf
configuration file contains directives of the following format:
.Bl -bullet
.It
.Ar src Ns / Ns Ar slen Cm deny Ar dst Ns / Ns Ar dlen
.Pp
If the source address of a query matches
.Ar src Ns / Ns Ar slen ,
and the translated destination address matches
.Ar dst Ns / Ns Ar dlen ,
deny the connection.
.It
.Ar src Ns / Ns Ar slen Cm permit Ar dst Ns / Ns Ar dlen
.Pp
If the source address of a query matches
.Ar src Ns / Ns Ar slen ,
and the translated destination address matches
.Ar dst Ns / Ns Ar 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
(if we reach the end of the ruleset)
the traffic will be denied.
.Pp
With inetd mode,
traffic may be filtered by using access control functionality in
.Xr inetd 8 .
.Sh EXIT STATUS
The
.Nm
utility exits with
.Dv EXIT_SUCCESS
.Pq 0
on success, and
.Dv EXIT_FAILURE
.Pq 1
on error.
.Sh EXAMPLES
Before invoking
.Nm ,
the
.Xr faith 4
interface has to be configured properly.
.Bd -literal -offset
# sysctl net.inet6.ip6.accept_rtadv=0
# sysctl net.inet6.ip6.forwarding=1
# sysctl 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
To translate
.Li telnet
service, and provide no local telnet service, invoke
.Nm
as follows:
.Bd -literal -offset
# faithd telnet
.Ed
.Pp
If you would like to provide local telnet service via
.Xr telnetd 8
on
.Pa /usr/libexec/telnetd ,
use the following command line:
.Bd -literal -offset
# faithd telnet /usr/libexec/telnetd telnetd
.Ed
.Pp
If you would like to pass extra arguments to the local daemon:
.Bd -literal -offset
# faithd ftp /usr/libexec/ftpd ftpd -l
.Ed
.Pp
Here are some other examples.
You may need
.Fl p
if the service checks the source port range.
.Bd -literal -offset
# faithd ssh
# faithd telnet /usr/libexec/telnetd telnetd
.Ed
.Ss inetd mode samples
Add the following lines into
.Xr inetd.conf 5 .
Syntax may vary depending upon your operating system.
.Bd -literal -offset
telnet  stream  tcp6/faith  nowait  root  faithd  telnetd
ftp     stream  tcp6/faith  nowait  root  faithd  ftpd -l
ssh     stream  tcp6/faith  nowait  root  faithd  /usr/sbin/sshd -i
.Ed
.Pp
.Xr inetd 8
will open listening sockets with kernel TCP relay support enabled.
Whenever a connection comes in,
.Nm
will be invoked by
.Xr inetd 8 .
If the connection endpoint is in the reserved IPv6 address prefix.
The
.Nm
utility will relay the connection.
Otherwise,
.Nm
will invoke service-specific daemon like
.Xr telnetd 8 .
.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
.%U http://tools.ietf.org/html/rfc3142
.%D June 2001
.Re
.\"
.Sh HISTORY
The
.Nm
utility first appeared in the WIDE Hydrangea IPv6 protocol stack kit.
.\"
.Pp
IPv6 and IPsec support based on the KAME Project (http://www.kame.net/) stack
was initially integrated into
.Fx 4.0 .
.Sh SECURITY CONSIDERATIONS
It is very insecure to use IP-address based authentication, for connections relayed by
.Nm ,
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 to 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 .
The IPv6 source address needs to be filtered using packet filters.
The documents listed in
.Sx SEE ALSO
have more information on this topic.