there are a few reports of curious HighDiscardRate events on the forum and a customer is seeing this event on most of his WS-C2950G-24-EI. The event is appearing in different time ranges on the 2 uplink ports of the device.
Currently my assumption is that it is caused by a wrap around of one of the counters that is used to calculate the discard rate.
I found some interesting facts:
- the InputPacketDiscardRate and the InputPacketRate do have bogus values of 1.7xxxE7
- I found 197 entries of this kind in the FH database for 'InputPacketDiscardRate' but only 4 different numeric values (from which 169 entries do have the same value)
- I do not find any curious OutputPacketDiscardRate but do also see a wrap around of the counters in the MIB (which could be a random issue)
I assume DFM still uses the 32-bit counter instead of the 64-bit counters for the gig Interfaces and does not have any mechanism to detect the wrap around of the counter.
I added the active and cleard DFM events as well as an snmpwalk of the ifTable (forgot to walk the ifMib for the high capacity counters...)
This bogus high utilization (or high discard rate) is a relatively common problem. Some causes have been device bugs where 64-bit counters wrap at 32-bit limits. Others seem to be obvious bugs with DFM, but EMC/Smarts is still investigating. The best thing to get for this is a sniffer trace showing at least two polling cycles when this bogus event occurs. Once we rule out a device issue, then you can talk to the TAC to gather other data for EMC.
We are pleased to announce availability of Beta software for 16.6.3.
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