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Ethereal-users: [Ethereal-users] how to analyse protocol data during a PPP over SSH VPN link

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From: Sia Duma <sia_duma@xxxxxxxxx>
Date: Sat, 12 Mar 2005 01:53:53 +0000 (GMT)
Dear Ethereal Support Team

I plan to use Ethereal to help me capture and analyse the network
data during a PPP over SSH VPN link that I am setting up for my
academic project on computer networking.

I am setting up a PPP over SSH connection to demonstrate a simple VPN
link between two computers on a LAN, running MAC OSX Panther.  To
prove that the link will remain Private, I want to show that any
correspondence between these machines is encrypted and that while the
VPN tunnel remains active, data cannot be seen from the outside, i.e.
from my laptop connecting to the same LAN. 

To achieve this, I installed Ethereal from a CD-ROM that came with a
book on Open Source Security Tools, on my laptop.  Ethereal installed
fine on XP, although I had to then download the WinPcap_3_1_beta4
file.  After I installed this, I had Ethereal working! 

I am new to analysing network data with packet capturing tools such
as Ethereal.  Can you please help me make this work?  I plan to set
up and capture the VPN link data next weekend at a friend's house,
connecting the two Macintosh OSX machines. 

Will Ethereal show the SSH encryption and tunneling protocols as they
go about setting up the encrypted tunnel in real time?  How can
Ethereal help me demonstrate that communication through the VPN link
is only visible between the SSH client and the server - but
inaccessible to the laptop, connected to the same LAN?

What settings or filters should I use in Ethereal for better results?
 How can I get Ethereal to capture only the protocols involved on the
setting up of the VPN link - and not other data on the network? 

On my laptop, I have a dual-bootable system with Windows XP and Red
Hat Linux 9 (although I have not yet installed Ethereal on the
Linux).  If I tried to connect from Linux SSH to the Macintosh OSX
SSH server (while it was connecting to the other Mac OSX SSH client)
- would this be an interesting way to test the VPN link?  How
different would the Ethereal results be if I tested the link from
Linux SSH - rather than from Windows XP?

Thank you very much in advance for your time taken to read this
message and for the time taken to help me. As I work full-time and
study part-time I will be grateful for your expert advice.

Kind regards

Sia


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