QoS rate-limit (CAR) vs service-policy (CBWFQ) in the same interface

Unanswered Question
Oct 9th, 2007

Hi everyone, does anybody know if is it posible or a best practice to police traffic in a interface using rate-limit, when there is already also a service-policy applied to that interface?

I have this problem too.
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Joseph W. Doherty Tue, 10/09/2007 - 11:56

Is there a reason why you wouldn't want to use a policer within the existing service-policy?

izael Tue, 10/09/2007 - 13:47

I?m traying to explain to my coworker that there is no need for an extra rate-limit command, since there?s already a service-policy on the interface, but since it is posible to add both commands to the same interface, I can?t find arguments to sustain my point. Does anybody know if there is a cisco recomendation abaut this issue?

Mohamed Sobair Tue, 10/09/2007 - 14:44

Hi,

I am not really sure about the recommendation but I can slite some differences between both rate-limiting & Policing as follows:

With Rate-limiting , when Multiple rate limit states are configured , the conform and exceed actions can also be continued to the next statment therfore a complex of rate policy could be configured.

With Plicing, you have the option to configure Police CIR , when this issued , it can be configured in Bps or percentage of the Interface Bandwidth.

Additional Option for Policing within the conform & exceed action , u can Set the Frame-relay De bit or Set ATM cell-loss priority values However , there is No continue action. also u have The Option Of Violation which defines traffic Rate above the Commited & Ecess burst rates.

For Cisco Recommendation, maybe some one On the forum can provide us with more details.

Regards,

Mohamed Sobair

Joseph W. Doherty Tue, 10/09/2007 - 15:13

Don't know if there any Cisco recommendation one way or the other. Would think the newer technique would be preferred. One issue that might arise if both commands use, would the CBWFQ before or after other policier?

Mohamed Sobair Tue, 10/09/2007 - 13:50

Hi,

I haven't seen some one yet using both, u are using MQC standard , why do u wanna go and use legacy CAR standard?

since u already have a policer applied, u can modify ur existing config and use Policing as well within the existing policy.

HTH

Mohamed Sobair

salolope Tue, 10/09/2007 - 19:25

izael,

It is recommended that you use only the MQC to police traffic. This is the preferred method for policing over legacy CAR since you can configure policing for multiple traffic and even up to three hierarchical levels (with the correct IOS version and hardware).

Enabling both on the interface might present a conflict in the rate of traffic that is being policed.

Please see this link:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos_c/fqcprt4/qcfpoli.htm

Most newer documentation does NOT include legacy CAR for policing.

HTH

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