Help with shape command MQC

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Aug 24th, 2010
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Ok. Here's the deal. I want to shape traffic using the shape command on a router, i might have very bursty traffic that will hammer the network for a small amount of time (30ms), and then be silent for a few seconds. This traffic doesn't depend on RTT.

I was thinking of creating my policy-map to shape the traffic to 5% of the line speed and then shape over the next 2 seconds. I assume that I would have to inscrese the size of the buffers to the maximum too.

So say at 10ms a huge burst of traffic came in that was matches in this class-map, would this then be sent for the next 2000ms (2s)? 

policy-map qos

class qos_class1

  shape average percent 5 2000 ms

  shape max-buffers 4096

Many thanks

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Giuseppe Larosa Wed, 08/25/2010 - 03:54
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Hello Golly,

the shaper will be always on at 5 percent of bandwidth of the link where the service policy is applied outbound.

with Bc and Be expressed in ms you are defining the size of the token buckets used to decide if traffic is conforming or is exceeding (so it needs to be stored for later sending this is shaping).

You don't need to use so big Bc and Be it is enough to accomodate 50 msec of traffic given the default of 4 msec as stated in command reference.

the shape max-buffers command decide the size in packets of the shaping queue (up to N packets can be held in the queue)

to be noted the command is not supported after 12.4(20)T that introduced Hierarchical QoS so check what IOS version is running on the device.

Hope to help


Lei Tian Wed, 08/25/2010 - 04:11
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Hi Golly,

As Giuseppe's mentioned, there is no need to change the shaper depth.

Just FYI, after 12.4(20)T, or in HQF model, you can change shaper depth using queue-limit command.


Lei Tian

golly_wog Wed, 08/25/2010 - 11:48
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Thank you very much for your replies, I actually tested this using a udp-jitter SLA and believe it is working.

I will be looking at HQOS when I get a chance and will let you know my findings.

Thanks again - I will be using 12.4.24T maybe...


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