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.IX Title "NAT-TRAVERSE 1"
.TH NAT-TRAVERSE 1 "2005-08-23" "perl v5.8.7" "User Contributed Perl Documentation"
.SH "NAME"
nat\-traverse \- Use of UDP to traverse NAT gateways
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&  user@left  $ nat-traverse 40000:natgw-of-right:40001
\&  user@right $ nat-traverse 40001:natgw-of-left:40000
.Ve
.SH "VERSION"
.IX Header "VERSION"
This document describes nat-traverse v0.4.
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
nat-traverse establishes connections between nodes which are behind \s-1NAT\s0
gateways, i.e. hosts which do \fInot\fR have public \s-1IP\s0 addresses. Additionally,
you can setup a small \s-1VPN\s0 by using pppd on top of nat-traverse (see
\&\*(L"\s-1EXAMPLES\s0\*(R").  nat-traverse does \fInot\fR need an external server on the
Internet, and it isn't necessary to reconfigure the involved \s-1NAT\s0 gateways,
either. \fInat-traverse works out\-of\-the\-box.\fR
.PP
See \*(L"\s-1TECHNIQUE\s0\*(R" for how this is achieved.
.SH "OPTIONS"
.IX Header "OPTIONS"
.ie n .IP """\f(CIlocal_port\f(CW:\f(CIpeer\f(CW:\f(CIremote_port\f(CW"" (required)" 4
.el .IP "\f(CW\f(CIlocal_port\f(CW:\f(CIpeer\f(CW:\f(CIremote_port\f(CW\fR (required)" 4
.IX Item "local_port:peer:remote_port (required)"
Sets the local port to use and the remote address to connect to.
.Sp
Note that you have to give the \s-1IP\s0 address or hostname of the \fI\s-1NAT\s0 gateway\fR of
the host you want to connect to, as the target host doesn't have a public \s-1IP\s0
address.
.ie n .IP """\-\-cmd=""\f(CIpppd...\f(CW""""" 4
.el .IP "\f(CW\-\-cmd=``\f(CIpppd...\f(CW''\fR" 4
.IX Item "--cmd=""pppd..."""
Runs the specified command after establishing the connection.
.Sp
The command will be run with its \s-1STDIN\s0 and \s-1STDOUT\s0 bound to the socket, i.e.
everything the command writes to \s-1STDOUT\s0 will be forwarded to the peer.
.Sp
If no command is specified, nat-traverse will relay input from \s-1STDIN\s0 to the peer
and vice versa, i.e. nat-traverse degrades to netcat.
.ie n .IP """\-\-window=\f(CI10\f(CW""" 4
.el .IP "\f(CW\-\-window=\f(CI10\f(CW\fR" 4
.IX Item "--window=10"
Sets the number of initial garbage packets to send. The default, 10, should
work with most firewalls.
.ie n .IP """\-\-timeout=\f(CI10\f(CW""" 4
.el .IP "\f(CW\-\-timeout=\f(CI10\f(CW\fR" 4
.IX Item "--timeout=10"
Sets the maximum number of seconds to wait for an acknowledgement by the peer.
.ie n .IP """\-\-quit\-after\-connect""" 4
.el .IP "\f(CW\-\-quit\-after\-connect\fR" 4
.IX Item "--quit-after-connect"
Quits nat-traverse after the tunnel has been established successfully.
.Sp
nat-traverse returns a non\-\f(CW0\fR statuscode to indicate that it wasn't able to
establish the tunnel.
.Sp
\&\f(CW\*(C`\-\-quit\-after\-connect\*(C'\fR is useful if you want another program to use the
tunnel. For example, you could configure OpenVPN to use the the same ports as
nat-traverse \*(-- thus OpenVPN would be able to cross \s-1NAT\s0 gateways.
.ie n .IP """\-\-version""\fR, \f(CW""\-\-help""" 4
.el .IP "\f(CW\-\-version\fR, \f(CW\-\-help\fR" 4
.IX Item "--version, --help"
.SH "TECHNIQUE"
.IX Header "TECHNIQUE"
nat-traverse establishes connections between hosts behind \s-1NAT\s0 gateways, without need
for reconfiguration of the involved \s-1NAT\s0 gateways.
.IP "1." 4
Firstly, nat-traverse on host \f(CW\*(C`left\*(C'\fR sends garbage \s-1UDP\s0 packets to the \s-1NAT\s0 gateway
of \f(CW\*(C`right\*(C'\fR. These packets are, of course, discarded by the firewall.
.IP "2." 4
Then \f(CW\*(C`right\*(C'\fR's nat-traverse sends garbage \s-1UDP\s0 packets to the \s-1NAT\s0 gateway of
\&\f(CW\*(C`left\*(C'\fR. These packets are \fInot\fR discarded, as \f(CW\*(C`left\*(C'\fR's \s-1NAT\s0 gateway thinks
these packets are replies to the packets sent in step 1!
.IP "3." 4
\&\f(CW\*(C`left\*(C'\fR's nat-traverse continues to send garbage packets to \f(CW\*(C`right\*(C'\fR's \s-1NAT\s0 gateway.
These packets are now not dropped either, as the \s-1NAT\s0 gateway thinks the packets
are replies to the packets sent in step 2.
.IP "4." 4
Finally, both hosts send an acknowledgement packet to signal readiness. When
these packets are received, the connection is established and nat-traverse can
either relay \s-1STDIN\s0 to the socket or execute a program.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
.Sh "Setup of a small \s-1VPN\s0 with \s-1PPP\s0"
.IX Subsection "Setup of a small VPN with PPP"
It's easy to setup a \s-1VPN\s0 (Virtual Private Network) by using the Point-to-Point
Protocol Daemon, \f(CW\*(C`pppd\*(C'\fR:
.PP
.Vb 7
\&  root@left # nat-traverse \e
\&      --cmd="pppd updetach noauth passive notty \e
\&             ipparam vpn 10.0.0.1:10.0.0.2"
\&      40000:natgw-of-right:40001
\&  root@right # nat-traverse \e
\&      --cmd="pppd nodetach notty noauth"
\&      40001:natgw-of-left:40000
.Ve
.PP
\&\f(CW\*(C`pppd\*(C'\fR creates a new interface, typically \f(CW\*(C`ppp0\*(C'\fR.  Using this interface, you
can ping \f(CW10.0.0.1\fR or \f(CW10.0.0.2\fR. As you can see, \f(CW\*(C`pppd\*(C'\fR upgrades the
data-only tunnel nat-traverse provides to a full \s-1IP\s0 tunnel. Thus you can
establish reliable \s-1TCP\s0 connections over the tunnel, even though the tunnel uses
\&\s-1UDP\s0!  Furthermore, you could even add IPv6 addresses to \f(CW\*(C`ppp0\*(C'\fR by running \f(CW\*(C`ip
\&\-6 addr add...\*(C'\fR!
.PP
Note though that although this \s-1VPN\s0 \fIis\fR a private network, it is \fInot\fR
secured in any way. You may want to use \s-1SSH\s0 to encrypt the connection.
.Sh "Port Forwarding with netcat"
.IX Subsection "Port Forwarding with netcat"
You can use \f(CW\*(C`netcat\*(C'\fR to forward one of your local \s-1UDP\s0 or \s-1TCP\s0 ports to an
arbitrary \s-1UDP\s0 or \s-1TCP\s0 port of the remote host, similar to \f(CW\*(C`ssh \-L\*(C'\fR or \f(CW\*(C`ssh
\&\-R\*(C'\fR:
.PP
.Vb 4
\&  user@left  $ nat-traverse 10001:natgw-of-right:10002 \e
\&        --cmd="nc -vlp 20000"
\&  user@right $ nat-traverse 10002:natgw-of-left:10001 \e
\&        --cmd="nc -vlp 22"
.Ve
.PP
As soon as the tunnel is established (using \s-1UDP\s0 ports \f(CW10001\fR and \f(CW10002\fR),
\&\f(CW\*(C`left\*(C'\fR's \s-1TCP\s0 port \f(CW20000\fR is forwarded to \f(CW\*(C`right\*(C'\fR's \s-1SSH\s0 Daemon (\s-1TCP\s0 port
\&\f(CW22\fR):
.PP
.Vb 2
\&  user@some-other-host $ ssh -p 20000 user@left
\&  # Will connect to right's SSH daemon!
.Ve
.PP
But do note that you lose the reliability of \s-1TCP\s0 in this example, as the actual
data is transported via \s-1UDP\s0. If you want reliable streams, use \s-1PPP\s0 on top of
nat\-traverse, as described above.
.SH "LIMITATIONS"
.IX Header "LIMITATIONS"
Only IPv4 is supported, nat-traverse won't work with IPv6 addresses. Even
though it would be relatively trivial to add IPv6 support, I refrained from
doing that, as there's no need to use \s-1NAT\s0 with IPv6 (the address space IPv6
provides is sufficient).
.PP
If you do need IPv6 support, drop me a note and I'll patch nat\-traverse.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
.IP "\s-1RFC\s0 1631 at http://www.ietf.org/rfc/rfc1631.txt" 4
.IX Item "RFC 1631 at http://www.ietf.org/rfc/rfc1631.txt"
The \s-1IP\s0 Network Address Translator (\s-1NAT\s0). K. Egevang, P. Francis.  May 1994.
(Obsoleted by \s-1RFC3022\s0) (Status: \s-1INFORMATIONAL\s0)
.IP "\s-1RFC\s0 3022 at http://www.ietf.org/rfc/rfc3022.txt" 4
.IX Item "RFC 3022 at http://www.ietf.org/rfc/rfc3022.txt"
Traditional \s-1IP\s0 Network Address Translator (Traditional \s-1NAT\s0). P.  Srisuresh,
K. Egevang. January 2001.  (Obsoletes \s-1RFC1631\s0) (Status: \s-1INFORMATIONAL\s0)
.IP "\s-1RFC\s0 1661 at http://www.ietf.org/rfc/rfc1661.txt" 4
.IX Item "RFC 1661 at http://www.ietf.org/rfc/rfc1661.txt"
The Point-to-Point Protocol (\s-1PPP\s0). W. Simpson, Ed.. July 1994.  (Obsoletes
\&\s-1RFC1548\s0) (Updated by \s-1RFC2153\s0) (Also \s-1STD0051\s0) (Status: \s-1STANDARD\s0)
.IP "<http://ppp.samba.org/>" 4
.IX Item "<http://ppp.samba.org/>"
Website of Paul's \s-1PPP\s0 Package (open source implementation of the
Point-to-Point Protocol (\s-1PPP\s0) on Linux and Solaris)
.IP "German talk about nat-traverse at http://linide.sourceforge.net/nat\-traverse/nat\-traverse\-talk.pdf" 4
.IX Item "German talk about nat-traverse at http://linide.sourceforge.net/nat-traverse/nat-traverse-talk.pdf"
Dieser Vortrag zeigt, wie man einen Tunnel zwischen zwei Computern, die
beide hinter NAT-Gateways sitzen, hinbekommt. Dazu wird ein neues Programm
vorgestellt, welches sowohl einfache Tastendrücke an die Gegenseite
weiterleiten, als auch beliebige Programme mit Verbindungen zur Gegenseite
starten kann. Damit ist ein einfaches \s-1VPN\s0 schnell aufgebaut.
.SH "AUTHOR"
.IX Header "AUTHOR"
Copyright (C) 2005 Ingo Blechschmidt, <iblech@web.de>.
.PP
You may want to visit nat\-traverse's Freshmeat project page,
<http://freshmeat.net/projects/nat\-traverse/>, for new releases.
.SH "LICENSE"
.IX Header "LICENSE"
This program is free software; you can redistribute it and/or modify it under
the terms of the \s-1GNU\s0 General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any later
version.
.PP
This program is distributed in the hope that it will be useful, but \s-1WITHOUT\s0 \s-1ANY\s0
\&\s-1WARRANTY\s0; without even the implied warranty of \s-1MERCHANTABILITY\s0 or \s-1FITNESS\s0 \s-1FOR\s0 A
\&\s-1PARTICULAR\s0 \s-1PURPOSE\s0.  See the \s-1GNU\s0 General Public License for more details.
.PP
You should have received a copy of the \s-1GNU\s0 General Public License along with
this program; if not, write to the Free Software Foundation, Inc., 51 Franklin
Street, Fifth Floor, Boston, \s-1MA\s0  02110\-1301, \s-1USA\s0.