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Cell Relay Retreat>MPLS-OPS Archive>month:2002-Oct> msg00154



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RE: Encapsulations

  • From: Anoop Ghanwani <anoop@lanterncom.com>
  • Date: Wed, 30 Oct 2002 13:33:50 -0800
  • Resent-Date: Wed, 30 Oct 2002 18:02:10 -0500
  • To: "'alok'" <alok.dube@apara.com>, mpls-ops@mplsrc.com

> just curious... so i ran this query on this list...
> 
> Why do most "encaps" define the upper layer payload?
> 
> for eg why does GRE define "ETypes" as a field etc?
> 
> we dont normally have one ETYPE talking to another one do we? 
> Apple talk
> terminates on Apple talk and IP on IP etc...
> 
> what does this field accomplish?

The type field is required because the tunnel is a
multiprotocol tunnel.  In other words, you could send
IP, AppleTalk and NetBIOS over the same GRE tunnel
between the 2 systems.  When the packet gets to the
other end of the tunnel, the receiving system needs to 
know which protocol to hand the packet to for processing.

-Anoop 

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