[c-nsp] storm-control errdisable with no traffic or vlan

Tom Hill tom at ninjabadger.net
Mon Aug 8 18:56:10 EDT 2022

On 2022-08-06 06:15, Saku Ytti via cisco-nsp wrote:
> On Sat, 6 Aug 2022 at 05:27, Paul via cisco-nsp
> <cisco-nsp at puck.nether.net> wrote:
>> Storm control pps is bugged on the 10g ports on the older 4900
>> platforms, 4948E , 4900M, sup6 platforms.
> My guess would be that PPS is not supported by the hardware and
> behaviour is undefined, and you would need to poke hardware to
> understand what was actually programmed when you asked it to PPS, i.e.
> it hasn't worked as desired in the 1GE either.

An aside, but an example of where this can go wrong...

I once came a-cropper of an Extreme X440 doing something interesting 
with its configured broadcast/multicast limits; if you configured 
'5000pps' as the storm-control limit, it would be divided by 1000 & 
measured every millisecond, so in fact the "real limit" was 5 frames per 
millisecond. This undocumented (at the time?) behaviour meant that any 
ports with multiple VLANs - especially those carrying FHRP - would 
immediately shutdown, because more than 5 multicast frames would be 
received more or less together.

The alternative is, of course, to have a counter that can be read/reset 
every second - but what if your ASIC can't do that?

Given the era of hardware, I do wonder if simply multiplying the 
configured storm-control limit by 10 will be sufficient to elect the 
exact same behaviour on the TE port. I'd hazard a guess that some bit of 
code is dividing by ten, and that's why it can't do 'per second' 
storm-control. I loved my 4900Ms muchly (gert is a big meanie) but I 
must confess I don't think I ever had (nor wanted) a customer-facing L2 
TenGig port.


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