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Community Member

Rate-limit burst- 3750

I want to rate-limit a vlan to 200Mbps on a 1Gbps link. All traffic above the 200Mbps should be dropped. I have questions about the burst rates:

1) Are the burst rates (normal and max) optional parameters ?

2) If not, how can they be stated to most strictly enforce the 200mbps limit ?

The equation I've been advised to use for "normal" configuration is:

burst= rate/8 * 1.5

maxburst= burst*2

This equation doesn't seem right for limiting to a strict 200Mbps.

Any good links or ideas would be appreciated.

Thanks,

4 REPLIES
Community Member

Re: Rate-limit burst- 3750

Does anyone know any good links for understanding the burst vs. the rate-limit

Community Member

Re: Rate-limit burst- 3750

If I read you correctly, you want a hard ceiling at 200M period. Without a burst headdomm..

rate-limit output 200000000 0 0 conform-action transmit exceed-action drop

Not sure If I'd do that... but.

Community Member

Re: Rate-limit burst- 3750

Hans-

Thanks for the reply...yes, I want a hard ceiling at 200Mbps...why would you hesitate to do that ? Perhaps I misunderstand the burst rate and how it should be used...but have found no clear explanation of how to apply this parameter correctly...do you have any suggestions, links ?

On a seperate note, I have found no cisco documentation on "rate-limit" command for the 3750, and have begun to wonder if the command is even supported...I know the "rate-limit" command was supported on older switches...What's strange is that the OS is actually accepting the command and seems to be partially working...

I'm running following IOS

WS-C3750G-24TS, 12.2(25)SEB4,C3750-IPSERVICES-M

Originally I thought that the burst-rate was causing a problem, allowing more data than the rate limit, but now I'm wondering if the rate-limit command is doing anything at all

Any thoughts ?

Thanks,

Bob

Community Member

Re: Rate-limit burst- 3750

Hi ,Boblutton,

just search the topic about CAR, hope this still help other on 2013 futher.haha....

http://www.cisco.com/en/US/docs/ios/12_2/qos/configuration/guide/qcfpolsh.html

Recommended Burst Values

Cisco recommends the following values for the normal and extended burst parameters:

normal burst = configured rate * (1 byte)/(8 bits) * 1.5 seconds

extended burst = 2 * normal burst

And other more info. in the link.

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