Excess burst size allocation in CAR

[ameen.ahmed]

Friends,

Normal burst size defines the size of token bucket which is the amount of data that can be sent in a given time interval.

Excess burst size defines  the amount of data that can be sent if no tokens are available in bucket per time interval. That means, in a given time interval, if the normal burst size is reached, it will borrow a token from excess burst bits.

As per Cisco standards,

Normal burst = CIR * Tc

Excess burst = 2 * Normal burst

For example, on a 1Mbps link, I'm limiting traffic to 512Kbps with 96KB as normal burst and 192KB as excess burst.

rate-limit output 512000000 96000 192000 conform-action transmit exceed-action drop

My questions is,

Does the above command means that I can send traffic with a max rate of 1Mbps since I set excess burst as 192KB ?

Thanks,

Ameen.

[Joseph W. Doherty]

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Posting

My questions is,
Does the above command means that I can send traffic with a max rate of 1Mbps since I set excess burst as 192KB ?

No, in actual fact your data transmission rate is always physical interface "speed".

What the policer will do, if you try to send a volume of data, during the measured time period (Tc), that exceeds what would be transmitted by the measured rate, the excess will be dropped.

PS:

BTW, Be often just seems to effectively create a larger Bc.