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Date: Thu, 9 Jun 2005 01:46:00 +0200
From: Jeremie Le Hen <jeremie@le-hen.org>
To: Greg 'groggy' Lehey <grog@FreeBSD.org>
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Cc: Marc Olzheim <marcolz@stack.nl>, FreeBSD-net@freebsd.org,
	Jeremie Le Hen <jeremie@le-hen.org>, Neo-Vortex <root@Neo-Vortex.net>
Subject: Re: Problems with gif tunnels
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Greg,

> My understanding is that GRE is to IP as PPP is to SLIP: it allows
> multiple protocols to be encapsulated.  I've done some tracing with
> Ethereal, and the only difference is a four-byte header in front of
> the payload for GRE; in an IP tunnel, it's simply missing.  I've
> written this up in my diary
> (http://www.lemis.com/grog/diary-jun2005.html#8), along with the
> traces.

yes it's usually a simple four-byte header when doing a simple tunnel.
But from what I have read [1] and according to what Giorgos said,
it seems it can be a lot more longer, depending on the value of the
five first bits of the GRE header.

Enjoy your tunnel ;-).

[1] http://www.networksorcery.com/enp/protocol/gre.htm
-- 
Jeremie Le Hen
< jeremie at le-hen dot org >< ttz at chchile dot org >