RE: Again with additional info: Problem trying to create 'pass through' with PuTTY and Dropbear




Hi Eric and the rest,

Thanks for your thoughts!

I understand your way of thinking, and it even makes me doubt my solution a bit.
Indeed, you could wonder how VNC server on PC A can listen on port 5900 while PuTTY is also using that port for communicating with the Dropbear server.

I hope and think that the way a tunnel is implemented in general, is in some way transparent to the operating system.
So I think that for a 'remote port forward', PuTTY isn't really listening on the local port that you have configured, but only makes sure in some way that the unencrypted traffic is delivered to that port number.

Anyone else?

Kind regards,
Rik.


Subject: RE: Again with additional info: Problem trying to create 'pass through' with PuTTY and Dropbear
Date: Thu, 18 Sep 2008 16:43:00 -0400
From: Eric.S@xxxxxxxxx
To: rikrik31@xxxxxxxxxxx

I am by no means an expert at any of this, and I have no knowledge of
Dropbear so please forgive me as I ask a few questions and possibly get
you thinking in a different way.

If PC A :5900 <-- Server 10001 using Dropbear (?), what is answering on
PC A; what application, VNC? If the VNC port 5900 is already in a
conversation with Dropbear or PuTTY or something else between PC A and
the Server, how can VNC answer when PC B calls? In the same respect,
how can PC B transmit on 5900, if it is also talking to the server from
its 5900 to the server 10001? How does Dropbear know to forward a
packets from PC B to PC A though the PuTTY SSH link?

If I am completely missing the picture, please let me know and I will be
happy to step aside and let someone more knowledgeable help.

Good Luck!

-Eric.

-----Original Message-----
From: listbounce@xxxxxxxxxxxxxxxxx
[mailto:listbounce@xxxxxxxxxxxxxxxxx]
On Behalf Of Rik Hennema
Sent: Thursday, September 18, 2008 3:43 PM
To: secureshell@xxxxxxxxxxxxxxxxx
Subject: Again with additional info: Problem trying to create 'pass
through'
with PuTTY and Dropbear


Hello,

I already posted this problem before, but haven't had any response so
far.
I added some details and additional information and tried to make it
more
clear to you.
Maybe, this time someone can help me out or at least give some hints
or
feedback?

The problem:

I'm trying to do the following:
I have a couple of 'client' pc's that are behind routers. I want to be
able to connect to them (using VNC) from anywhere when needed without
having to open up ports on the routers. Therefore, the connection
needs to be
initiated from the client side (thus from behind the routers).
My plan is to let those clients set up and keep open an SSH connection
to a server on the Internet that I have access to (running Dropbear as
an SSH server).
The clients I want to take over, are running a startup script creating
the connection and keeping it open. Over the connection, a tunnel is
then created from client port X, to server port Y. From my PC I then
create an SSH connection to the server and create a tunnel from PC
port Z to server port Y.

I'm currently testing this setup on my LAN using PuTTY on two Windows
pc's
(one acting as the server and one acting as the client) and a Linux
server (S) running Dropbear. One pc
(A) is running VNC Server. The other PC (B) is running the vnc viewer.
I use PuTTY to create an SSH connection from PC A to the server (S)
and
create a *remote* forward from server port 10001 to PC A, port 5900
(this
is where ultra VNC is listening).
Then, I use PuTTY to create an SSH connection from PC B to the server
(S)
and create a *local* forward from PC B, port 5900 to server port
10001.

After this, I start Ultra VNC viewer on PC B and connect it to
'::5900'.
Now, I'm getting the following connection error: "Connection failed -
Error
reading Protocol Version".
I have tried Putty 0.58 and 0.60. Using both versions gives the same
error
message in Ultra VNC.

I have no problems connecting directly from PC B to PC A ('::
5900').

To make sure it isn't an Ultra VNC problem, I set up the same tunnels
(but
using port 23 instead of 5900) and then used telnet to connect from
one host
to the running telnet server on the other host.
The screen goes black (dosprompt under Windows XP) until I press a
key,
then I get back my prompt. Nothing happens.
I also used Wireshark (network sniffer) on the server side and no
packets were
captured (not even in promiscious mode).

Is my set-up technically possible? So should I be able to set up those
tunnels
as a kind of 'pass-through' mechanism?

Does anyone have a clue about what I'm doing wrong or forgot to do?

Kind regards,
Rik.
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