On Wednesday, 8 June 2005 at 12:40:53 +0200, Jeremie Le Hen wrote: >>> It's currently pushing 7:30 pm, and I was going to send out a reply >>> tomorrow. But indeed, it seems that Linux people prefer GRE tunnels, >>> we prefer (with good reason) IP tunnels, and the whole issue was one >>> of documentation. After changing my tunnel from GRE to IP, it worked >>> (and works) like a charm. > > IIRC, > - Linux uses the ipip module to do IP-over-IP tunnel > - FreeBSD uses the gre(4) interface to do GRE tunnels > - GRE is a Cisco product and means ``Generic Routing > Encapsulation''. I don't know what they mean with the term > "Generic" because I have only seen IP encapsulated tunnel so far. > According to the GRE header, I guess GRE is far more powerful > than a simple IP-over-IP encapsulation, and I would be glad if > someone could explain us what are the benefits of this protocol. > I would conclude by saying that indeed Linux users tend to use > GRE tunnels whereas a IP-over-IP tunnel would be enough, because > they used to be trendy. > >> What is the difference between gre and gif tunnels anyway... the man mages >> were not that informative... > > Read above. Usually gre(4) tunnels are used as simple IP-over-IP tunnel, > so a gif(4) would do the same with less overload (due to GRE header size). > GRE seems far more powerful, but I don't know its benefits.
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. Greg -- The virus contained in this message was not detected. Finger [EMAIL PROTECTED] for PGP public key. See complete headers for address and phone numbers.
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