From: CCIE 4 Me (ccie4me@inbox.lv)
Date: Sat Mar 04 2006 - 16:24:18 GMT-3
IE's solution is correct. What the scenario want to achieve is a "maximum of
500kbps". Since rate is an increament of 8k, we then have a CIR of 496000,
with 4000 as the leftover to makeup the max of 500kbps, you can then use the
leftovers as the value for Bc (normal burst), since you want to maintain a
max of 500kbps, you must not allow for excess burst, there Be will be equal
to Bc..ie
!
rate-limit output access-group 100 496000 4000 4000 conform-action
transmit exceed-action drop
!
Should be the correct response. Even if one make the mistake and type in
!
rate-limit output access-group 100 500000 4000 4000 conform-action
transmit exceed-action drop
!
The router will be kind enough to correct it. When you go back to look at
your configure, the router will change it to:
!
rate-limit output access-group 100 496000 4000 4000 conform-action
transmit exceed-action drop
!
HTH
----- Original Message -----
From: "Reinhold Fischer" <Reinhold.Fischer@gmx.net>
To: "PANDI MOORTHY" <moorthypandi@gmail.com>
Cc: "Cisco certification" <ccielab@groupstudy.com>
Sent: Saturday, March 04, 2006 2:48 PM
Subject: Re: how to choose Rate-limt brust
> 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_item09186a0
0800cdfab.shtml#policing
>
> http://tinyurl.com/ouvcf
>
> 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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