Re: CAR

here is the forumla from the doccd:

http://www.cisco.com/en/US/customer/docs/ios/qos/command/reference/qos_q1.html#wp1083294

Policing Traffic with CAR

CAR embodies a rate-limiting feature for policing traffic. When policing
traffic with CAR, Cisco recommends the following values for the normal and
extended burst parameters:

normal burst (in bytes) = configured rate (in bits per second) * (1 byte)/(8
bits) * 1.5 seconds

17.000.000 * (1 byte)/(8 bits) * 1.5 seconds = 3.187.500 bytes

extended burst = 2 * normal burst

2 * 3.187.500 = 6.375.000 bytes

With the listed choices for parameters, extensive test results have shown
CAR to achieve the configured rate. If the burst values are too low, then
the achieved rate is often much lower than the configured rate.

For more information about using CAR to police traffic, see the "Policing
with CAR" section of the "Policing and Shaping Overview" in the *Cisco IOS
Quality of Service Solutions Configuration Guide*.
Examples

In the following example, the recommended burst parameters for CAR are used:

Router(config)# *interface serial6/1/0*

Router(config-if)# *rate-limit input access-group 1 17000000 3187500 6375000
conform-action transmit exceed-action drop*

THE MQC 'police' using the same value in the doccd of 8000 bits does
calucuate the same bc in the above example forumla though:

R1#sh policy-map interface f0/0
 FastEthernet0/0
  Service-policy output: CAR_PM
    Class-map: class-default (match-any)
      67 packets, 7167 bytes
      5 minute offered rate 0 bps, drop rate 0 bps
      Match: any
      police:
          cir 8000 bps, bc 1500 bytes
        conformed 0 packets, 0 bytes; actions:
          transmit
        exceeded 0 packets, 0 bytes; actions:
          drop
        conformed 0 bps, exceed 0 bps

INCREASE it to your example and it does not follow the forumla anymore, i
guess this is a more detailed internal forumla to the IOS that is not
documented on the doccd with the example:

http://www.cisco.com/en/US/customer/docs/ios/qos/configuration/guide/traffic_policing_ps6441_TSD_Products_Configuration_Guide_Chapter.html#wp1019829

R1#sh run policy-map
policy-map CAR_PM
 class class-default
   police cir 17000000
     conform-action transmit

R1#sh policy-map interface f0/0
 FastEthernet0/0
  Service-policy output: CAR_PM
    Class-map: class-default (match-any)
      34 packets, 3755 bytes
      5 minute offered rate 0 bps, drop rate 0 bps
      Match: any
      police:
          cir 17000000 bps, bc 531250 bytes
        conformed 0 packets, 0 bytes; actions:
          transmit
        exceeded 0 packets, 0 bytes; actions:
          drop
        conformed 0 bps, exceed 0 bps

 --
Garry L. Baker

"With sufficient thrust, pigs fly just fine..." - RFC 1925

On Tue, May 31, 2011 at 12:16 AM, Raghav Bhargava <
raghavbhargava12_at_gmail.com> wrote:

> Hey Experts
>
> I am sure many must have asked this before, but i need some help in CAR.
> Below is the syntax while using CAR.
>
>
>
> rate-limit input/output access-group ## { max amt of bw in bits } { normal
> burst in bytes } { excess burst in bytes } conform-action .....
> exceed-action ......
>
>
> Now if the max amt of bw is 10mbps. Since using CAR we have to convert it
> in
> bits . Therefore 10 mbps = 10000000 bits.
>
> And to calculate normal burst it is max amt of bw in bits/8 and to convert
> it in bytes divide the outcome by 8.
>
> Please correct me on this calculation . This is where i am not sure whether
> i am doing it right or wrong.
>
> --
> Warm Regards
> Raghav
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html

Blogs and organic groups at http://www.ccie.net
Received on Tue May 31 2011 - 01:06:28 ART