[c-nsp] CEF wrong next hop

[Tim Devries]

Yeah, I did see on Cisco.com that the problem could be caused by having
proxy arp enabled (which it wasn't).  Your theory sounds very plausible to
me though, as I'm lacking any other possible explanation.  

Thanks for the information.

Tim

-----Original Message-----
From: Gert Doering [mailto:gert at greenie.muc.de] 
Sent: Sunday, October 03, 2004 1:02 PM
To: Tim Devries
Cc: 'Rodney Dunn'; 'cisco-nsp at puck.nether.net'
Subject: Re: [c-nsp] CEF wrong next hop



Hi,

On Thu, Sep 23, 2004 at 09:09:55AM -0300, Tim Devries wrote:
> Cisco Internetwork Operating System Software
> IOS (tm) 7200 Software (C7200-P-M), Version 12.3(10), RELEASE SOFTWARE
(fc3)

This is not an "upgrade" from 12.3(7)T, but actually going to a wholly
different IOS train (12.3 main), with lots less features and (usually)
also far less bugs.


As to the original issue: I've seen this effect in the past myself in
"some early version of 12.0S" - a not-directly-connected host ended
up in the ARP table of a router, and thus in the CEF table, packets
being forwarded directly onto the LAN, instead of to the correct
next-hop router.  I assume the problem happed because an ARP request
or ARP reply "leaked" across VLANs (so the router in VLAN x saw some
ARP packets related to the host in VLAN y), but I've never been able 
to reproduce it on purpose.

gert
-- 
Gert Doering
Mobile communications ... right now writing from * back @ home *