Catalyst 4500 QoS

Unanswered Question
Dec 6th, 2007

I am looking to create a QoS policy on a Cat 4500 which will limit traffic leaving a fastethernet port to 20Mb/s. Based on this 20Mb/s I then want to apply a shape percentage to each of the 4 tx queues and transmit tcertain traffic in each queue. I would like to match traffic from a subnet elsewhere in my network and put it in a tx queue with, for example, 25% of the rate I limit the interface to.

Am I able to shape the interface to 20Mb/s and base percentage values on this 20Mb/s for each tx queue ?

Thanks, Stephen.

I have this problem too.
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bvsnarayana03 Thu, 12/06/2007 - 20:29

Is there a specific reason to limit a fa or gi interface to 20Mbps.

You may create a policy-map with 4 classes & then limit the trafic on each queue by policing to required rate.

hope that clarifies.

mheusing Fri, 12/07/2007 - 04:17


Have a look at the "Configuring QoS" section of the Catalyst 4500 configuration guide

There are Guides for different IOS versions, I picked one of them.

There is a description about how to configure traffic shaping with the 4 queues, which will allow you to implement your requirement:

"Allocating Bandwidth Among Transmit Queues"

which tells you about how to setup minimum bandwidth guarantees and "Configuring Traffic Shaping of Transmit Queues"

which is about shaping each queue to a specified rate.

As far as I know there is no nested policy, which will allow you to specify a rate for the interface and percentages for each queue based on the rate. Rather you can specify a limit per queue and as long as the sum of those rates is 20 Mb you should get the desired result.

Hope this helps! Please rate all posts.

Regards, Martin

StevieOliver_2 Fri, 12/07/2007 - 04:25


I had read the first 2 links you posted. I was really interested in nesting policies with percentages based on an interface value which doesn't seem possible. This was to save me re-adjusting each queue's alloacted bandwidth when I increase the overall link bandwidth. For instance I have a fastethernet port going at 10Mb/s. I was hoping to use percentages of that such that if I open the link up to be able to transmit 20Mb/s then the percentages increase the queue sizes proportionately. The reason I am limiting the fastethernet port is that the transmission network it connects into only allocates 10Mb/s now and soon to be 20Mb/s.

I will just have to re-config each tx queue when the bandwidth increases.

Thanks, Stephen.


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