Re: GRE tunnel

From: istong@stong.org
Date: Thu Nov 13 2003 - 09:22:42 GMT-3


  Hi,

   Assuming that Cisco follows the standard - here is some
information.
   A GRE packet is composed of a header in which a type
field specifies
   the encapsulated protocol (ARP, IP, IPX, etc.). See
RFC2784 for
   details about the encapsulation.

   A packet tunneled with a GRE encapsulation has the
following format:
   the delivery header is an IP header whose destination is
the tunnel
   end-point (FBIP), followed by a GRE header specifying the
link-layer
   type of the unidirectional link.

            ----------------------------------------
            | IP delivery header |
            | destination addr = FBIP |
            | IP proto = GRE (47) |
            ----------------------------------------
            | GRE Header |
            | type = MAC type of the UDL |
            ----------------------------------------
            | Payload packet |
            | MAC packet |
            ----------------------------------------

Thanks,

Ian
www.realccie.com

> sorry for the of-topic but may be someone can help
> me find more about GRE keepalive.
> i have linux that can work with GRE tunnel. this days i
> need this linux to support GRE keepavlive. i cant find any
> RFC or Cisco document that have details about the
> keepalive packet/header format, can any one knows where
> can i find more about this issue. i know the Cisco docs
> about how to configure the GRE keepavlive but in this docs
> no packet format is presented.
>
> TIA
>
> Roi
>
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