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QoS SRR Shaped and Shared

Unanswered Question
Feb 7th, 2006
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I am trying to understand how SRR Shaped and Shared work together. Example:

interface g1/0/1

srr-queue bandwidth share 10 50 25 25

srr-queue bandwidth shape 2 0 0 0

Since I have configured both shaped and shared the first queue in the shared will be ignored.

So will share calculate its B/W percentages like the following?

50/(50+25+25) = 50% 25/(50+25+25) = 25% 25/(50+25+25) = 25%

If so is this going to share the whole 1gig of B/W or only share 500M since the shape is configured to use 50%(1/2) and is essentially “guaranteed”. If my thinking is wrong please advise on how these two work together. Any assistance/guidance is greatly appreciated. Thanks in advance

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Overall Rating: 5 (2 ratings)
pkhatri Tue, 02/07/2006 - 11:39
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The shared queues will be guaranteed the appropriate proportion of the remaining 500Mb. However, that does not mean they are limited to that. That just gives a minimum limit on how much they are entitled to. Dynamically, if the first queue is using less than its allotted 500Mbps, the other queues will equally share this excess bandwidth amongst themselves. In an extreme case, if the first queue is not running any traffic at all, the other three could be sharing 1Gbps. On the other hand, if the first queue is running at 500Mbps, the other three share the remaining 500M in proportion.

Hope that helps - pls rate the post if it does.


frankbr77 Wed, 02/08/2006 - 07:45
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one more quick question. Can you configure the shaped queue to be anything other than the first queue? Thanks for you help with this.


pkhatri Wed, 02/08/2006 - 11:48
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Hi Brad,

While I've never done that myself, my understanding is that you can configure any of the queues for shaping with the proviso that all of the shaped queues are lower numbered than any of the shared queues. That is, if you configure queue 2 for shaping, queue 1 must also be configured for shaping. In other words, starting from queue 1, there must be a consecutive set of shaped queues followed by all the shared queues. Therefore, the following is allowed:

shared, shared, shared, shared

shaped, shared, shared, shared

shaped, shaped, shared, shared

shaped, shaped, shaped, shared

shaped, shaped, shaped, shaped

Anything else is not.

Hope that helps - pls rate the post if it does.



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