[c-nsp] Sup720 software forwarding

[Brian Turnbow]

Hi,


> 
> On 03/08/2013 07:46 AM, Peter Rathlev wrote:
> > Theoretically, if one would happen to have a Sup720 that 
> does software 
> > forwarding, how is it that one can check what the reason 
> for punts is?
> 
> An excellent question. In the past, TAC have found stuff like 
> this with ELAM captures, but it's never been obvious to me 
> how they inferred the "cause" from the ELAM output; I assume 
> they have a cheat sheet somewhere with a bunch of hex values on it!
> 
> If there's no obvious cause, it could be a TCAM mis-program; 
> we've had a series of these over the last few years where the 
> box sporadically fails to correctly program the PFC or one of 
> the DFCs. It seems this condition is completely invisible 
> except for its effects - that is, the Sup doesn't seem to be 
> able to detect it. I guess this means the HW FIB can be 
> written but not read?
> 
> Anyway, these can be a super-bitch to troubleshoot; we've 
> seen ones that affect a single IPv4 prefix, ones that affect 
> a single MPLS label, and ones that affect a single adjacency 
> entry. They're usually triggered by something local to the 
> box (e.g. our last was triggered by moving an SVI from one 
> VRF to another) - to the best of my knowledge we've never 
> seen one triggered by an "external" event e.g. routing update.
> 
> Typically a linecard or chassis reboot is the only way to 
> clear them; no amount of "clear blah" will help, which is 
> extraordinarily irritating...


We have found that you can "fix" single prefix or mpls labels by 
Removing the route from the box (i.e not propogating it to the box)
Waiting about 10 minutes
Reinserting the route

I have never figured out what the "excact" time is or what needs to timeout but something does.
A quick remove replace does not work
Best guesss is that it remains programmed in the hardware for a certain time before being removed for good.

At least this has worked for us in the past and we haven't needed to reboot





Brian

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