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Re: Layer 2 crypto device needed.
From: "Mitchell Rowton" <mrowton () bdo com>
Date: Wed, 31 Mar 2004 15:53:39 -0500

I think this will be difficult to do without using a layer three device.
 The military uses layer 2 devices like this, but at some point during
the encrypt/decrypt process it needs to be translated to a serial pipe. 
So even though it is layer two encryption, we had to use routers to
translate serial to ethernet at some point in the process.  And if you
have to use routers anyway...  Could you just use a VPN?  Mind you,
there may be new spiffy technologies that translate strait ethernet, but
they are at least not common.

Another point is that the STP will only be passing data when the fiber
is down.  I assume this won't happen often, and therefore your exposure
is lower than if the primary path was also STP.  Now if an attacker knew
this they could cut the fiber link in order to sniff the STP, I would
assume someone would start tracing this cable fairly quickly to figure
out what the problem is, and thus find the attacker.  Bottom line is
that I would also consider the following three options (1) Using routers
/ VPN  (2) Using another fiber run as backup and removing the bridges 
(3) Accepting the risk

--
Mitchell

Oleksandr Darchuk <o.darchuk () wucb lviv net> 03/31/04 09:53AM >>>
Hello, list

There are 2 remote offices and 2 links betwen them: fiber-optic and
twisted pair. And there are 2 separate VLANs in both offices, that's
why
remote offices communicate on Layer 2 (Ethernet frame, especially
802.1q). The "primary" line is fibe-optic.
I want to create backup line for fiber-optic using twisted pair.
Fiber-optic link is terminated on switch, so I think that best way to
set-up backup line is to terminate twisted pair (using Ethernet
bridges)
on the same switch and use STP for backup. But I think it's not secure

sending Ethernet frames through twisted pair.

So the question is: does anyone know Layer 2 devices (like Ethernet 
bridges) with any crypto algs (with pre-shred key or smart card or 
anything else). I googled some time, but didn't find anything.

Thanks for all advises.



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