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The meaning of burst size in policy map config?

I Need to restrict upload speed with my 3560 and I'm going to do it with policy maps. If I want to configure interface so that it would have upload speed of 4Mbps what would be a good burst size? I planned to do it like this:

class-map match-all rate-limit

match ip dscp default

policy-map 4Mbps

class rate-limit

police 4096000 192000 exceed-action drop

I also need to make an interface where upload speed would be 30 Mbps what would be a good burst size for that? Should it be a lot higher? If so why?

3 REPLIES

Re: The meaning of burst size in policy map config?

Hi,

burst size with a single rate policer is needed because of a small "issue". The point is: no sender can send a frame at 4 Mbps, when the line speed is f.e. 100 Mbps. Frames are always sent with line speed.

So the policer needs to be configured with a value defining for how long it is OK to send above the defined rate (to burst) - one frame (at least!), two frames, several kBytes, etc.

As the name implies, this defines the "burstiness" of the accepted traffic. The defined policer rate is the "long term average". The burst value defines what "long term" means.

Regards, Martin

New Member

Re: The meaning of burst size in policy map config?

So in practice is it better to have huge burst size or small? So when I use huge burst size the "saw tooth" effect is bigger than when using smaller burst size?

Should I use bigger burst sizes when configuring speeds like 20 - 40 Mbps than when configuring speeds like 2 or 4 Mbps?

Any experiences what would be a good burst size when a customer has a lot of video traffic?

New Member

Re: The meaning of burst size in policy map config?

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