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CAR - Committed Access Rate

Hello all,

hope someone can clarify me a few things about this topic.

Lets start with this configuration snippet, we have a serial interface configured for CAR:

interface serial 0/1

     rate-limit output 128000 10000 20000 conform-action transmit exceed-action drop

As far as I know the above config would set the maximium allowed bw out of serial 0/1 to 128kbit/s, set the normal/excess burst size to 10kbyte/20kbyte. Traffic conforming is allowed the rest is dropped.

1) I don't understand the meaning of the burst size

2) What happens if I get a normal/excess burst greater than the value specified?

Any hint is appreciated

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VIP Expert

Re: CAR - Committed Access Rate

Hi,

There are 2 type of burst sizes.  The first one is normal burst, in your case 10000, which allows only some packet to excess 10000 bytes.  The second one is excess burst, which allows all packet to burst up to 20000 bytes. So, your rate is 128000 Bits per second and if you need to you can go up an additional 20000 bytes before all packets are dropped.

Here is link to Car for more info:

http://www.cisco.com/en/US/docs/ios/11_1/feature/guide/CAR.html

HTH

Reza

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