Posted Thu, 01 Jan 2015 06:00:00 GMT by Portal Admin

Q. My switches are always orange and showing lots of errors (or discards). Why?

A. We frequently hear of devices that appear to have high levels of discards and/or errors. They are usually orange on the map, and the status window shows a message like this:

Reason: Discards = 738: [1] sc0

The most likely reason that InterMapper shows a high rate of discards from a device is that the device is actually reporting these errors. It's common that when InterMapper reports errors (from its SNMP queries), the manufacturers' own monitoring tools will report zero errors. (It's also normal that the affected devices are operating normally, without problems, in this state.)

Experiments and Workarounds:

* Use the vendor's own network monitoring tool (by telnetting in, using a web browser, etc.) to see if errors are being reported through the native management interface. It's possible that there actually is a problem.

* This may be a bug in the SNMP implementation of the device. You can check with your vendor to see if there's a firmware upgrade that addresses the problem.

* To test InterMapper's accuracy, use another SNMP tool to check out the particular MIB variables for the device. InterMapper monitors the ifInDiscards and ifInErrors MIB variables (and the corresponding ifOutxxxx variables) to compute its error and discard figures. You can monitor these same variables with your own SNMP tool to see if the same errors are reported there.

* Examine the device's packet loss statistic in the Status Window.

- If packets are actually being discarded, you'll see a higher than normal packet rate of dropped packets.
- If packets aren't being dropped, it's another clue that the values reported by SNMP are incorrect.


* As a workaround, if you've satisfied yourself that the error reports are bogus, you can instruct InterMapper to ignore the discards and/or errors. To do this, choose Set Info > Set Behavior and check the "Ignore Interface Errors" or "Ignore Interface Discards" box as desired.

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