High cpu utilization in switches

Unanswered Question
Jan 15th, 2010

Hi,

I usally get customer calls saying there is high cpu utilization but when we check the show proc cpu it does not reflect any processes taking very high utilisation. Can any1 help in monitoring these CPU utilisation in switches.specially in chassis based switches.

What all steps should be taken to find the root cause?

Regards

Amar

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Overall Rating: 3 (2 ratings)
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lusandi Fri, 01/15/2010 - 15:57

Hello,

Can you ask your customer when is he getting the high cpu utilization message?

if there is something diferent happening on the lan or if he is using some debugs?

Ganesh Hariharan Sat, 01/16/2010 - 02:18

Hi Amar,

Genrally high CPU utilization in switches are caused by following reason.

In some network deployments, a busy CPU is normal. In general, the larger the Layer 2 or Layer 3 network, the greater the demand on the CPU to process network-related traffic. These are examples of operations that have the potential to cause high CPU utilization:

Known symptoms that can occur when the switch CPU is too busy:

•Spanning-tree topology change—When a Layer 2 network device does not receive timely spanning-tree BPDUs on its root port, it considers the Layer 2 path to the root switch as down, and the device tries to find a new path. Spanning tree reconverges in the Layer 2 network.

•Routing topology change, such as BGP route flapping or OSPF route flapping.

•EtherChannel links bounce—When the network device at the other end of the EtherChannel does not receive the protocol packets required to maintain the EtherChannel link, this might bring down the link.

•The switch fails to respond to normal management requests:

–ICMP ping requests.

–SNMP timeouts

–Telnet or SSH sessions that are slow or cannot be started

•UDLD flapping—The switch relies on keepalives from its peer in aggressive mode.

•IP SLAs failures due to SLAs responses beyond the acceptable threshold.

•DHCP or IEEE 802.1x failures if the switch cannot forward or respond to requests.

•Dropped packets or increased latency for those packets routed in software.

•HSRP flapping.

If in future customer says high cpu problem just check with the following command which process id is taking CPU utilization to find out the really cause.

Show process cpu

Hope that helps out your query !!!

Regards

Ganesh.H

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