From: Alex De Gruiter \(AU\) (Alex.deGruiter@didata.com.au)
Date: Wed Jun 28 2006 - 20:15:36 ART
Hey guys,
I have been working on some GRE-based scenario in the labs, and have
come across a particular solution from Cisco that I have reason to
question. I post to the group as I would like some clarity on my
understanding of GRE.
The crux of the problem is as follows: A headquarters site needs to pass
IP Multicast traffic over IPSec to a remote site, and so must
encapsulate the traffic inside a GRE packet before transmission.
The associated Cisco document is here:
http://www.cisco.com/univercd/cc/td/doc/product/core/7100/swcg/6342gre.h
tm#1057710
My problem is that the tunnel interface at headquarters (172.17.3.3/24)
is on a different subnet to the tunnel interface at the remote site
(172.24.3.6/24). I don't see how this can work, and how IP traffic can
be passed across the GRE tunnel. I have tried this in the lab and my
only conclusion is that the tunnel interface IP addresses must be in the
same net. To make things even more confusing, a Figure in this document
(reference 3-2) references the tunnel IP addresses as, indeed, being on
the same subnet.
Can someone wiser than I comment?
Thanks in advance,
Alex de Gruiter
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