Re: inter-site WAN security question

If you have network A and network B connected to each other via a VPN link (say, via a router at each network), where hosts on network A can talk to hosts on network B over the VPN tunnel, then someone sniffing the traffic in between can tell that router A and router B are talking, but can't tell which host from network A is talking to which host on network B, or what they're saying.


nobledark@xxxxxxxxxxxx wrote:
Hi Andrew, thanks for the quick reply..

So if I understand you correctly, if someone were sniffing on a router between the two sites and the VPN was in tunnel mode then they would not be able to see the source and destination IP's - is that correct?

Sorry, a bit ignorant about the inner workings of IPSEC VPNs...what about during the initial tunnel establishment - how does the vpn server at s1 know the path to the vpn server at s2?

Thanks again...

On Wed, 04 Jul 2007 15:33:06 -0400 Andrew Harris <andrew.f.harris@xxxxxxxxx> wrote:
The question you want answered is based on the implementation of the VPN.
If the VPN is using IPSec's Tunnel mode, headers & the payload are
encrypted/encapsulated. If just using Transport mode, only the payload is
encapsulated so the IP appear in plaintext. So to answer your question, if
using Transport mode, then the hacker would be able to see the that S1 and
S2 are in communication. In Tunnel mode, the hacker would have a very hard
time and then the weakness of the security lies in the IPSec encryption
itself (how long it takes to crack that...).

Hope this helps

On 7/4/07, nobledark@xxxxxxxxxxxx <nobledark@xxxxxxxxxxxx> wrote:

1st post - I had a hypothetical question poised to me that I
not answer so I thought that I would ask the list. Here's the

- Two sites, s1 and s2
- s1 and s2 have the need for a bi-directional WAN link
- The WAN link would be secured via a VPN and all traffic would
tunneled through the VPN
- Both sites are connected via broadband links; s1 is on a cable
modem and s2 utilizes a factional T-1.
- There are 5 hops between s1 and s2.

Given this scenario, the question was, how anonymous can the
connection be between these sites? Put a different way, assuming
that s1 and s2 are secure and not under hacker control, how much

a threat is there of a 3rd party monitoring the traffic stream
the route between the sites and discovering that they are
to each other?


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