WAN link should not exceed 70 percent utilization

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Apr 16th, 2009
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1. Where can i find a document in CISCO site saying WAN link should not exceed 70 percent utilization. Should the WAN link exceed the treshold 70 percent level, end user need to upgrade the bandwidth of the link.

2. I need to send the above document/reference to customer. A reference from cisco will have weight to the customer.


Nazli ;-)

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nazlishahmuhamad Thu, 04/23/2009 - 23:37
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Thank you Belal Farouk for your reply. It is a new info for me for the CPU recommended treshold utilization is 70%.

Yes my end user complaining that the leased line is having problem (slow/flapping). Okay, as provider we check our part. However, i also want my end user to have to check on their router part.

i read from the link above that cisco recommends a value 70% for CPU. However it does not clear in the CISCO document if the CPU value above 100% will cause slow/flapping to the router.

I believe the 2 issues are related.

1) CPU utilization 70% - CISCO recommend to upgrade router

2) link utilization 70% - CISCO recommend to upgrade the link

Otherwise the router will experience slow/flapping if the the CPU and link reach 100% utilization.

I will re-search again on the above issue in the cisco website as to provide the info to my end user.

"...and people just want to live happily ever after" ;-)

bfarouk Fri, 04/24/2009 - 06:28
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It is a two different things that you are stating. When you say leased line, it should be UP (not reset) regardless of router is being using CPU 100%. You can find the particular interface information with "Show Controller or Show Serial," it can hint you CRC error or some sort of error to cause reset. It may be your circuit issue or Serial card in router is being the problem. Serial card can be looped and generate test also your Telco can loop to find out.

If both confirmed good then proceed with router's CPU and memory configuration to find out process switching or fast switching problem.


nazlishahmuhamad Sun, 04/26/2009 - 16:55
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Point taken. We will check portion by portion to resolve the issue. We will check on the leased line (NT to NT) and end user (router + serial V.35 cable) .

I always thought CPU utilization and link utilization at 100% level will effect the router with slow/flapping issue. I guess it is just an urban legend. ;-)

We will treat the quality issue (CRC error + other error) and the slowness of the link as separated issue.

Again thank you for your valuable input.



Joseph W. Doherty Sat, 05/02/2009 - 05:06
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I don't recall a Cisco recommendation about link utilization.

However, beyond about 70% utilization you may encounter significant queuing. Whether you do depends on the nature of the traffic. Whether it's an issue, depends on the nature of the application.

Sometimes additional bandwidth is needed, but often bandwidth management, via QoS, works as well or better.


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