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QoS bandwidth limitations

I'm configuring QoS on my switched network using Catalyst 2950 IOS 12.1(22)EA13 and Catalyst 2960 IOS 12.2(52)SE.

From release notes I read that the 2960´s use SRR (for shaping and sharing) on it's queues witch can be configured in "shaped mode" or "shared mode".

The 2950's don't use this algorithm thus cannot be configured with any of those modes.

My question is:

By defining a policer that limits the available bandwith for one traffic class, I'm limiting the available bandwith for other classes (on 2950's that is...)??

Is there a "work-around" for this problem??

"In shaped mode, the egress queues are guaranteed a percentage of the bandwidth, and they are rate-limited to that amount."

"In shared mode, the queues share the bandwidth among them according to the configured weights. The bandwidth is guaranteed at this level but not  limited to it. For example, if a queue is empty and no longer requires a  share of the link, the remaining queues can expand into the unused  bandwidth and share it among them."

This was copied from the cisco release notes but I read some other documents (cisco and others) that made me think otherwise.

thanks in advanced for reply

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Cisco Employee

Re: QoS bandwidth limitations

Hi,

By defining a policer that limits the available bandwith for one traffic class, I'm limiting the available bandwith for other classes (on 2950's that is...)??Is there a "work-around" for this problem??

I am not awear of this limitation. 2950 supports per class policing. Did you test it or you found it in document?

"In shaped mode, the egress queues are guaranteed a percentage of the bandwidth, and they are rate-limited to that amount."

"In shared mode, the queues share the bandwidth among them according to the configured weights. The bandwidth is guaranteed at this level but not  limited to it. For example, if a queue is empty and no longer requires a  share of the link, the remaining queues can expand into the unused  bandwidth and share it among them."

That is correct for switches supports SRR queue model.

Regards,

Lei Tian

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