Grant bandwidth (CBWFQ?)

Unanswered Question
Jun 24th, 2010
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Hi Team,

i am new to the community so i greet you all!


My doubts and problems are related to the need to shape the traffic of a class granting a minimum bandwidth.


We have a 7206-VXR so we have Gigabit physical interfaces, our SP is granting 200Mbps.


The shape is working fine but the bandwidth command don't trigger couse, for my router, there's no congestion.


I think that this is a common problema and maybe i am trying to solve in the wrong way.


Any suggestion is appreciated


Thanks in advance


Denis

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amahendi Sat, 07/17/2010 - 09:21
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  • Cisco Employee,

Hi Denis,


Shaping using the 'shape' cli defines the max rate for a class; whereas, the 'bandwidth' cli defines the minimum bandwidth guarantee for that class under functional congestion.


For example,


policy-map test

class A

  shape average percent 20

class B

   bandwidth percent 10

  class C

    bandwidth percent 30



- Traffic through class A will *always* get shaped to 20% of intf bandwidth. Doesn't matter whether the interface is congested or not.

- Traffic through class B and Class C will get a *minimum* guarantee of 10 and 30% of intf bandwidth when the interface is congested. When the interface is not congested, then there is really no need for a queueing policy (~ bandwidth cli) and the queueing part of the policy won't kick in. So, class B / class C can basically use the entire intf bandwidth if there is no traffic through the other (bandwidth) classes. However, should the physical interface be congested (tx_ring is full) then queueing kicks in and each class is given a minimum guarantee that's configured. The remaining bandwidth is shared amongst the bandwidth classes in the ratio of guarantees.


- Abhi

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