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11-15-2010 11:22 AM
11-15-2010 11:22 AM
High latency to procurve switch management IPs
Is there some reason the switch is so slow to return a ping to it's own mgmt ip?
I wouldn't care about it, but it makes it harder to monitor network health when the switches themselves show high latency.
any help would be appreciated...
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11-16-2010 01:59 AM
11-16-2010 01:59 AM
Re: High latency to procurve switch management IPs
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11-16-2010 08:07 AM
11-16-2010 08:07 AM
Re: High latency to procurve switch management IPs
measuring ICMP round trip times is not a reliable indicator about switch health, because ICMP packets will be answered with a low priority. Did you check CPU load and free packet buffer for IP management to ensure that the switch has enough system resources to answer the ICMP packets?
Cheers,
Michael
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11-16-2010 08:25 AM
11-16-2010 08:25 AM
Re: High latency to procurve switch management IPs
the swtich proc is hovering near 6-10% and there is 24MB of free ram. 2500 packet buffers free.
These are mosly edge swtiches connected via fiber 1000sx. They only have about 6 access points connected to each of them and not much else. Performance is not my worry -- Link health is my big concern.
But my monitoring software shows my switches with the highest latency -- that's misleading since the devices behind the swtich have very low latency. I don't understand why the swtich would be so slow to return pings.
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11-16-2010 11:00 AM
11-16-2010 11:00 AM
Re: High latency to procurve switch management IPs
While my email ends in .hp.com, the switches are almost as much a black box to me as anyone else. One experiment you could try is see if something like linkloop (on HP-UX, and a port for Linux exists), which is a Layer-2 "ping" to which ProCurves will respond shows the same high RTT. You might have to get an idea of the rtt by using the time command against the linkloop command on UX - linkloop doesn't (iirc) calculate/return an RTT.
Also, you could find a ping program that would let you send two (or more, but bounded to a small number) of ICMP Echo Requests at the same time. If the RT latency of the second (or Nth) is much lower than the latency of the first, that suggests aggressive interrupt coalescing.
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11-18-2010 06:19 AM
11-18-2010 06:19 AM
Re: High latency to procurve switch management IPs
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11-18-2010 06:34 AM
11-18-2010 06:34 AM
Re: High latency to procurve switch management IPs
Basically the switch is able to forward and return a packet from a connected device faster than it's own IP stack can respond to a ping.
Granted that ping replies from a switch should be at a lower priority than fowarding traffic, but it really seems excessively slows. It'll go from 1ms to 30ms to 64ms etc.
Note this doesn't happen on all of my switches either - mainly just the newer ones. The older 800m's seems to be fine.
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