Giuseppe Larosa Fri, 05/01/2009 - 03:22
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Hello Mahesh,

rate-limit is the command that enables CAR = committed access rate.

CAR can be used for the following:

to limit inbound or outbound traffic

to mark traffic.

CAR action can be on all traffic or only on traffic that matches an ip acl.

Multiple CAR commands can be used but cannot be really nested.

Nowdays CAR is seen as a legacy QoS tool for performing policing and marking.

A service policy command applies a policy map to an interface.

A policy map is a modular QoS object.

Each policy map can reference other objects called class-maps.

A class-map is a traffic class that can be defined in different ways including using an ACL, matching ip precedence or DSCP, CoS or invoking NBAR.

the policy-map references one or more classes for each class it can define one or more actions.

Among the possible actions there are:

CB shaping

CB policing (this compares to CAR)

CB marking (again this compares to CAR).



not all of this actions can be configured together and depends also on direction of application (you cannot shape inbound)

there is always a default-class that includes every flow that hasn't matched the previous classes.

So we can say that MQC modular QoS provides a framework to use tools that once were configured using separate commands.

the MQC provides a single approach on how to associate traffic to classes.

another important difference is that MQC supports multi level hierarchy a parent policy can invoke another policy map as the action associated to one of the classes.

For more information you can see the QoS config guide

Hope to help


mahesh-gohil Sun, 05/03/2009 - 21:35
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thanks for reply,

Means in ISP we are not using any QOS so rate-limit will be OK for ISP customers and for MPLS where we are using modular qos so service-policy will be ok

or is there any advantage or pros/cons of using service policy instead of rate0limit for ISP customers

Thanks in advance


Giuseppe Larosa Sun, 05/03/2009 - 22:49
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Hello Mahesh,

CAR has been widely deployed by service providers to enforce sub-rate contracts and/or to perform marking.

To be noted that CAR supports also MPLS exp marking as well.

The reasons can be historical: CAR has been deployed first and used on internet access.

MPLS services have been deployed later.

Or it can be also a question of policies: if you just want to rate-limit all traffic on a link CAR can be a good choice.

Actually, with MQC you can perform all the actions that CAR can do.

Hope to help


mahesh-gohil Sun, 05/03/2009 - 23:13
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yes your are right

But here in CAR we do not have option for violate action transmit/drop



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