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Network Performance Monitors Showing in excess of 100% utilization

Can someone please help resolve a disagreement here.  We have a Cisco CAT 5509 with several VLans set up.  All of the ENet ports are 10/100 along with several fiber Giga ports.

Out network performance monitor (Solarwinds) is showing that quite frequently we are well in excess of 100% utilization (as high as 400%).  My network analyst says that is because that even though the ports are 10/100, the actual routing supervisor can't handle more than 10 Meg and the traffic is queued up.

I have trouble buying it.  Why would Cisco have a switch with boards capable of running at 10/100/1000, but a supervisor unable to route the VLans at more than 10 Meg.  Secondly, perhaps I'm just being too logical, but how can you get more than 100% utilization?  It seems like either the tool (Solarwinds) is reporting incorrectly ... or the speed we are saying the port is running at (10 Meg) is incorrect.  If the speed is actually running at 100 Meg, then the performance of 40% is more understandable.

Any thoughts?

2 Solutions
Don JohnstonInstructorCommented:
The backplane on the 5509 is made up of 3 seperate 1.2gb buses. Depending on which slot a card is in will determine which bus is used. The big question is how much traffic are you pushing through the backplane.

A single 12 port 100mbps line card could put the bus utilization at 100%. That would, or course require all 12 ports to be transmitting at the same time. Make it two 24 port 100mbps line cards and it's not hard to see how you could max out the utilization.

As for why Cisco would have a switch like that... It's an old switch chassis. Back when it was designed, they probably never considered that there would be 24 port 100mbps lines cards. Remember that pesky 640K RAM boundary on the first IBM PC? At the time I'm sure they thought "who would ever need more than 640K of RAM!".

I seriously doubt the bottleneck is in the supervisor engine or route processor though.


It depends which supervisor is in your 5509, but the Supervisor 3 can run up to 3 Gb/sec. NONE of them are limited to 10 Mb/sec. Where are you measuring your data exactly? On the port? I suspect that Solarwinds is assuming that a 100mb port is only 10mb, so the 100% threshold is lower than it should be- a software configuration issue, not a switch issue. Type "show port x/x" on the switch and it will tell you what speed and duplex it's actually running at.

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