Trunk Port Threshold Best Practice?

Unanswered Question
May 28th, 2007

Using CiscoWorks LMS and I notice the notification threshold for switch port utilisation is set at 40%. I know I've seen this before, but I can't remember why 40% was the magic number. I've Googled and come up with nothing useful so I'm handing it over to the experts :)

Does this have something to do with this value being an "average" rather than a peak? I'm struggling to understand why, in a fully switched network, 40% utilisation is something to be concerned about.

Hope you can improve my education :)



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Overall Rating: 4 (2 ratings)
mohammedmahmoud Tue, 05/29/2007 - 00:20


You shouldn't worry at all, this Utilization Threshold is the upper threshold for link utilization expressed as a percentage of the total bandwidth as a part of the Ethernet interface performance characteristics. The default is 40%. This is the threshold where the notification is triggered in order for you to be notified that the utilization has exceeded this value, it has no impact it is just for notification.

HTH, please do rate all helpful replies,

Mohammed Mahmoud.

ben_johnson Tue, 05/29/2007 - 15:37

Thanks Mohammed.

I think I may have chosen my words poorly.

What I'm really trying to understand is this:

In a full-duplex, microsegmented network, which is essentially a collision-less environment, wouldn't it make more sense to set a utilisation threshold of around 80%? In that case, you'd actually be getting close to saturating your bandwidth and creating a bottleneck.

At 40% utilisation, especially on a trunk port which you'd expect to run at a higher utilisation, you still have quite a large portion of free bandwidth.

I'm still relatively new to the networking game, so I'm trying to get my head around something that others seem to take for granted. The question is really more general, about the 40% utilisation threshold figure, than about CW LMS specifically.



mohammedmahmoud Tue, 05/29/2007 - 23:28


I think that you are talking logical and have a point of view, despite this being the default on the CW LMS, in our company we do monitor our trunk links with 80% threshold, the defaults are not always the best choice, may be this default was intended for access ports having end users, and of course its not logical to have an End user with 80% utilization on his access port as a normal situation.


Mohammed Mahmoud.


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