2007 Jun 25 - Mon
Cisco Device Health
In Cisco's book, Top Down Network Design, one useful show command is 'show buffers'.
Some useful SNMP statistics include:
- BusyPer. CPU busy percentage in the last 5-second period.
- AvgBusy1. 1-minute exponentially decayed moving average of the CPU busy percentage.
- AvgBusy5. 5-minute exponentially decayed moving average of the CPU busy percentage.
- LocIfInputQueueDrops. The number of packets dropped because the input queue was full.
- LocIfOutputQueueDrops. The number of packets dropped because the output queue was full.
- LocIfInIgnored. The number of input packets ignored by the interface.
- BufferElMiss. The number of buffer element misses. (You can also check misses for small, medium, big, large, and huge buffer pools.)
- BufferFail. The number of buffer allocation failures.
I've been doing most of my snmp statistics gathering on 5 minutes intervals. On some
interfaces, it may be of value to step that up to 1 minute intervals. Of course, if my
total collection time is over 1 minute, I may have problems with that.
From the same book, is this interesting statistic about why Window's file transfers over
WAN links can go only 'so fast'. SMB acts like a ping-pong protocol. It can only send up
to 32KB before requiring an acknowledgement. So if the delay is 50 ms end to end, and
ignoring client and server delays, a client can receive at most 32 KB every 100
milliseconds, or 320 KB per second. This means that the maximum throughput is 2.56 Mbps, at
best.
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