[c-nsp] CEF wrong next hop

[Rodney Dunn]

Rob,

I think that today the cef inconsistency checker just
detects for inconsistent information between
the RP and the LC's like on a 75xx or GSR.
It today doesn't do anything to correct the situation.
There is talk about having it do that at some point.

This sounds like a recursion problem.

The customer that hit the CSCee74177 bug never loaded
the debug image DE has put together to find root cause.

Can you post the 'sh ip route' and then a 'sh ip route'
for each next hop route then the 'sh ip cef'?

Can you easily reproduce it?

Thanks,
Rodney


On Wed, Sep 22, 2004 at 08:13:58PM +0000, rwcrowe at comcast.net wrote:
> In the meantine while you identify if it is a bug or not, you can turn on the cef consistency check to try to correct the information.
> http://www.cisco.com/en/US/partner/tech/tk827/tk831/technologies_tech_note09186a00800946f7.shtml
> --
> Rob Crowe 
> rwcrowe at comcast.net
> 
> 
> -------------- Original message -------------- 
> 
> > 
> > In 12.3(7)T1 we've noticed a problem running CEF whereby 
> > certain routes show the incorrect next hop (i.e. different from the routing 
> > table) and result in routing loops. According to this document 
> > (http://www.cisco.com/en/US/tech/tk827/tk831/technologies_tech_note09186a008 
> > 00cdf2e.shtml) this could occur if the routes were discovered via proxy arp 
> > on the interface. This is not the situation in our case, though the 
> > _results_ are quite similar. 
> > 
> > This bug: 
> > http://www.cisco.com/cgi-bin/Support/Bugtool/onebug.pl?bugid=CSCee74177&cco_ 
> > product=IOS&fset=CEF/DCEF/FIB&swver=12.3&keyw=&target=7&train=T1 
> > 
> > is actually quite similar compared to what we are seeing, however unlike 
> > that bug, when we kill CEF on our router the routing then returns to normal 
> > (next hop learned via BGP), and all is well in the universe. I am wondering 
> > if anyone else has seen the same or similar bug on the T train, as we also 
> > have the same issue with another route on a router running version 
> > 12.2(17a). 
> > 
> > I'm assuming for the moment that it is a bug, simply because the behaviour 
> > seems strange, and the bug is listed as not reproducible, and it is so very 
> > close to our situation. As well, I do not think it is normal for CEF to 
> > have differing next hops from the entries in the routing table. 
> > 
> > Any advice would be appreciated, even if it is just to confirm that this is 
> > a bug. 
> > 
> > Thanks, 
> > 
> > Tim Devries 
> > 
> > 
> > 
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