10-24-2008
ssh X-forwarding and remote forwarding behind proxy
Hi,
from my workplace we use a proxy to connect to the outside world, including external ssh servers.
The problem is that the server is seeing the connection coming from the proxy and knows nothing about the client behind it. The ssh connection itself works fine, but x-forwarding does not work as expected. In my opinion this is because the server is trying to use the display of the proxy and not the one of the client.
Same issue with remote port forwarding, when someone uses the remote port I think the ssh server forwards the request to the proxy and not to the real client.
I have found two workarounds to solve the x-forwarding issue:
-create a VPN between the client and the server, and do the x-forwarding inside the VPN (which is similar to a LAN)
-install a VNC server on the ssh server, a VNC client on the ssh client and do a local port forwarding, then connect to localhost:xxxx
I'm sure the VPN solution will fix the remote forwarding as well, but... is there a way to get around these issues without using other software, maybe some kind of environment variables to set in OpenSSH?
Thanks.
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SSLH(1p) User Contributed Perl Documentation SSLH(1p)
NAME
sslh - Switch incoming connection between SSH and SSL/HTTPS servers
SYNOPSIS
sslh [ -v ] [ -p [host:]port ] [ -t timeout ]
[ --ssh [host:]port ] [ --ssl [host:]port ]
DESCRIPTION
sslh is a simple script that lets you switch an incoming connection on a single port between distinct SSH and SSL/HTTPS servers.
sslh listens for connections on a port and is able to redirect them either to an HTTPS web server or a SSH server.
This lets one setup both a HTTPS web server and a SSH server and access them through the same host+port.
OPTIONS
The program follows the usual GNU command line syntax, with long options starting with two dashes.
-p, --port [host:]port
The port the proxy will listen to. If no port is given, 443 is used by default. If no host is given, "localhost" is used by default.
-s, --ssh [host:]port
The SSH server which the SSH connections must be forwarded to. If omitted, the default is localhost:22.
-l, --ssl, --https [host:]port
The HTTPS server which the HTTPS connections must be forwarded to. If omitted, the default is localhost:443.
-t, --timeout delay
Timeout in seconds before a silent incoming connection is considered as a SSH connection. The number can be fractional.
The default is 2seconds.
-v, --verbose
Verbose output. This option can be used several times for more verbose output.
EXAMPLE OF USE
Is this tool actually useful? Yes.
For example one can use it to access both a SSH server and a secure web server via a corporate proxy that only accepts to relay connections
to port 443. Creating a tunnel that passes SSH connection through a CONNECT-enabled web proxy is easy with connect-tunnel (also included in
the "Net::Proxy" distribution).
The proxy will let both SSH and HTTPS connections out (since they all point to port 443), and the home server will connect those incoming
connections to the appropriate server. This only requires to run the HTTPS server on a non standard port (not 443).
TECHNICAL NOTE
How can this proxy find out what kind of protocol is using a TCP connection to port 443, without being connected (yet) to the server? We
actually rely on a slight difference between the SSL and SSH protocols (found thanks to ethereal):
SSH Once the TCP connection is established, the server speaks first, presenting itself by saying something like:
SSH-2.0-OpenSSH_3.6.1p2 Debian 1:3.6.1p2-1
SSL With SSL, it's always the client that speaks first.
This means that sslh can be used with any pair of protocols/services that share this property (the client speaks first for one and the
server speaks first for the other).
AUTHORS
Original idea and C version
Frederic Ple "<sslh@wattoo.org>".
Perl versions
Philippe 'BooK' Bruhat "<book@cpan.org>".
SCRIPT HISTORY
Version 0.01 of the script was a quick hack designed in 2003 as a proof of concept.
Version 0.02 (and higher) are based on "Net::Proxy", and included with the "Net::Proxy" distribution. Version 0.02 didn't work, though.
Version 0.03 correctly initialised the "in" connector.
Version 0.04 lets the proxy listen on any address (instead of "localhost", which is still the default). Thanks to Dieter Voegtli for
spotting this.
SEE ALSO
Net::Proxy, Net::Proxy::Connector::dual.
COPYRIGHT
Copyright 2003-2006, Philippe Bruhat. All rights reserved.
LICENSE
This module is free software; you can redistribute it or modify it under the same terms as Perl itself.
perl v5.10.1 2009-10-18 SSLH(1p)