[c-nsp] GRE tunnels between Cisco ME3600X

[paul.magee at agencyport.com]

It certainly sounds like a plausible explanation. I guess my next
question is can I force a CEF punt?

-----Original Message-----
From: Gert Doering [mailto:gert at greenie.muc.de] 
Sent: 17 April 2012 14:10
To: paul.magee at agencyport.com
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] GRE tunnels between Cisco ME3600X

Hi,

On Tue, Apr 17, 2012 at 01:40:46PM +0100, paul.magee at agencyport.com
wrote:
> I have a GRE tunnel established between two of these things, they show

> up in each other's CDP neighbours, a BGP session is established 
> between them, and they are exchanging routes. BGP learned routes are 
> inserted into the routing table but it doesn't seem to actually route 
> through the tunnel, as though for some reason, the route in the 
> routing table is ignored. If I add a static route to the remote tunnel

> address, both it & the learned route are immediately dropped from the 
> routing table. On a probably related note there is no arp entry for 
> the remote tunnel address on either router...

This sounds like "the control plane knows how to do GRE, but the
forwarding plane does not".  

So your BGP and CDP speaker can insert packets into the tunnel, but the
hardware forwarding engine has no idea how to handle that - and while it
could give the packet to the CPU to handle it, it sanely decides to not
do that.

But that's just guesswork.

gert
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