Rate Limit Command

[PinkLips]

Anyone familiar with the rate-limit command to limit bandwidth on an interface? Below is an example that I found. I checked with cisco TAC but it still does not make sense. What does the config below do?

interface fa0/0
ip address x.x.x.x y.y.y.y
rate-limit input 2200000 312000 470000 conform-action transmit exceed-action drop

rate-limit output 2200000 312000 470000 conform-action transmit exceed-action drop

Thanks,
Nicole

 

[Nazgulero]

Hello,

this CAR configuration basically rate-limits both input and output traffic to 2200000bpbs, with a normal burst size of 312000 bytes, and an excess burst size 470000 bytes. Everyting above this rate will be dropped...
Does this not work for you ?

Regards,

GP

 

[lambent]

what do you mean by "does not make sense"?

 

[PinkLips]

this CAR configuration basically rate-limits both input and output traffic to 2200000bpbs, with a normal burst size of 312000 bytes, and an excess burst size 470000 bytes. Everyting above this rate will be dropped."

Sorry..I'm new to all this.
I understand that it limits input\output to 2.2mbps.
But what do you mean by burst rate and excess burst rate?
If you have a pipe that's 3mbps and you limit traffic to 2.2mbps, should the setting for the burst rate and excess burst rate be higher than 2.2mbps?


Thanks,
Nicole

 

[lambent]

There's actually a Cisco recommendation on these burst rate and excess burst rate settings but of course it's not mandatory to follow the recommendation.

normal burst = CIR * (1 byte)/(8 bits) * 1.5 seconds
excess burst = 2 * normal burst

In your case, CIR is 2200000,
so normal burst = 412500,
and excess burst = 825000

Again you really don't have to follow this.

And if possible, would you describe how it doesn't make sense? Did you actually try the command and find that it didn't do what you want?

 

[PinkLips]

Thanks Lambent,I guest my quetions can be re-stated as "what is the definition of normal burst and excess burst rate?" Burst is a frame relay term right? Is burst the maximum amount of data that can be transmitted within an X amout of time?

Thanks,
Nicole

 

[lambent]

I think you'll love this powerpoint presentation:

http://www.internetworkexpert.com/resources/01700368.htm