IPSec, GRE, and Transport Mode

From: John Neiberger (neiby@xxxxxxxxxx)
Date: Wed Mar 13 2002 - 15:32:53 GMT-3

   
I'm looking at an example on CCO that is encrypting a GRE
tunnel, but this is the first time I've noticed the addition
of 'mode transport' in the configuration.

I was under the impression that transport mode was for use only
when the tunnel endpoints were creating the traffic. Does that
apply here because the router endpoints are creating the GRE
packets and are therefore the end hosts? That kind of makes
sense.

What would be the functional different in this case between
tunnel mode and transport mode? If we're using a GRE tunnel,
would there be any significant difference? Any gotchas
regarding either method with GRE?

Thanks,
John <-- IPsec neophyte

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