Re: Shaping - identical Bc & Be values

Hi Matt,

I think you might be getting confused between shaping and policing. My understanding is as follows:

If you are shaping then the size of the token bucket is (Bc) + (Be). For (Be) to be "disabled" it would need to be 0. If (Be) is >0 then there is room for extra tokens to build up and you will be able to send more than (Bc) in an interval.

If you are using a Single-Rate, 3-Color Policer you have 2 buckets  a (Bc) bucket and a (Be) bucket. Tokens can only be removed from one bucket per interval so if the (Be) bucket is the same size as the (Bc) bucket then you can't send any more than (Bc) bytes per interval effectively disabling excess burst.

In your example excess burst is NOT disabled. After a quiet period where tokens can build up, you would be able to send up to 128000 bits in a single interval.

cheers,
Ben.

From: Matt Sherman <matt.sherman2_at_gmail.com<mailto:matt.sherman2_at_gmail.com>>
Reply-To: Matt Sherman <matt.sherman2_at_gmail.com<mailto:matt.sherman2_at_gmail.com>>
Date: Thursday, 21 June 2012 10:00 AM
To: Cisco certification <ccielab_at_groupstudy.com<mailto:ccielab_at_groupstudy.com>>
Subject: Shaping - identical Bc & Be values

Hello,

I was wondering if someone could clear this up for me. I've seen it
written that if the normal burst (Bc) and excess burst (Be) values are
equal, then excess
burst is not allowed. So in the examples below, if the Bc and Be values
are both 64000, does that mean there is no excess burst?

GTS based Shaping

Router(config-if)# traffic-shape rate 256000 64000 64000
Class-Based Shaping with a policy-map:
Router(config)# policy-map MYPOLICY
Router(config-pmap)# class MYMAP
Router(config-pmap-c)# shape 256000 64000 64000

Thanks,
Matt

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Received on Thu Jun 21 2012 - 23:23:09 ART