From: Reinhold Fischer (Reinhold.Fischer@gmx.net)
Date: Sat Mar 04 2006 - 16:48:43 GMT-3
Hi Pandi,
i came across the following statement in the book 'IP Quality of Service' (Ciscopress, Page 38):
<cite>
- Rate (bps) should be in increments of 8 Kbps, and the lowest value allowed for conformed and extended burst size is 8000 bytes.
- The minimum value of BC size is Rate (bps) divided by 2000. It should be at least 8000 bytes.
- The BE is always equal to or greater than the BC value.
</cite>
According to the calculation the BC value would be: 500000 / 2000 = 250
So i would choose the recommended minimum value of 8000 bytes for BC and
twice the size for BE:
access-list 100 permit tcp any any syn
access-list 100 deny ip any any
int e0/0
rate-limit output access-group 100 496000 8000 16000 conform-action
transmit exceed-action drop
There is another formula on cco on this URL:
http://www.cisco.com/en/US/tech/tk543/tk545/technologies_q_and_a_item09186a00800cdfab.shtml#policing
which you can use to calculate the BC/BE values. This formula assumes
a typical round-trip-time of 1.5 seconds and therefore the results
for BC/BE produce higher numbers.
When using this formula the BC value would be 93750 and the BE value
would be 187500.
hope this helps and is not too confusing :-)
regards
Reinhold
On Sun, Mar 05, 2006 at 12:36:02AM +0800, PANDI MOORTHY wrote:
> Hi
>
> The question is to limit the TCP sync traffic to 500kbps which is out from
> the Ethernet interface.
>
> So I have to use the rate-limit command to achieve this, one thing still I
> can't figure out is choosing the value for burst-normal and burst-max,
> Anyone please advice me on this?
>
> Regards.
> Pandi
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