From: Jaycee Cockburn - BCX SS (Jaycee.Cockburn@bcx.co.za)
Date: Fri Nov 11 2005 - 11:11:05 GMT-3
Hi All,
May I be nasty...rfc2784...
http://www.rfc-editor.org/rfc/rfc2784.txt or
http://www.javvin.com/protocolGRE.html
Or
A GRE encapsulated packet has the form:
---------------------------------
| |
| Delivery Header |
| |
---------------------------------
| |
| GRE Header |
| |
---------------------------------
| |
| Payload packet |
| |
---------------------------------
1. The IP address of the tunnel is in the payload part
2. No, see rfc
3. I think if you read the rfc you'll understand, but how I understand
is the router determines it must route the packet out tunnel 0, so it
generates the packet, sees that it must go out a GRE interface, so adds
the gre header, and then adds the normal ip header of the interface used
as the tunnel source with a destination of the tunnel destination...
Hope this makes sense...
Cheers
JC
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
CCIEin2006
Sent: 11 November 2005 03:45 PM
To: ccielab@groupstudy.com
Subject: Re: GRE packet structure and order of operations
Anyone want to take a stab at this?
On 11/10/05, CCIEin2006 <ciscocciein2006@gmail.com> wrote:
>
> Hi folks,
> Can someone kindly provide some clarification on how GRE works:
> 1. Where does the IP address of the Tunnel interface appear in the
> packet?
> 2. Anyone have a good link showing a GRE packet with all the source
> and destination IP addresses (in the encapsulated IP packet, GRE
> header, and transport IP header?) 3. If possible explain step by step
> the order of operations i.e step 1 the packet is routed to the tunnel
> interface, step 2 the encapsulated packet is routed out the physical
> interface with the source IP changed to the tunnel source IP, etc...
> Thanks!
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