From: alsontra@hotmail.com
Date: Fri Jan 23 2004 - 15:33:25 GMT-3
So basically Cisco did some statistical analysis and came up with this
formula as a general guide line, but individual calculation are based upon
specific use and protocol behavior. Great!
One more thing, in IOS 12.2 do you know what the expectable ranges for rate
or bc and be are? And are they specified in bits or bytes.
Thanks
Alsontra Daniels
----- Original Message -----
From: "Bob Sinclair" <bsinclair@netmasterclass.net>
To: <alsontra@hotmail.com>; <>
Sent: Friday, January 23, 2004 6:23 AM
Subject: Re: Policing
> Alsontra,
>
> The burst value in policing is designed to work with the TCP windowing
> algorithm to help make it possible to actually reach the policed rate.
> Remember that whenever a TCP packet gets dropped it will trigger the TCP
> slow start algorithm on the sender. This will make the sender back off
its
> sending rate. If you allowed no burst, you would find that, on average,
TCP
> traffic will be below the policed rate.
>
> The rules of thumb for these settings are derived from experiment and
> statistical analysis. In the real world, you "should" set the burst
based
> on the specific characteristics of the TCP application(s) you are
policing.
>
> HTH,
>
> Bob Sinclair
> CCIE #10427, CISSP, MCSE
> www.netmasterclass.net
>
> ----- Original Message -----
> From: <alsontra@hotmail.com>
> To: <ccielab@groupstudy.com>
> Sent: Thursday, January 22, 2004 1:32 PM
> Subject: Policing
>
>
> > Hello All,
> > I'm finding the calculations for CAR based policing a
little
> > confusing. I've read through the Cisco Policing and Shaping Overview,
but
> > can't seem to understand normal and extended burst calculations. Cisco
> > recommends following values when policing:
> >
> > normal burst = configured rate * (1 byte)/(8 bits) * 1.5 seconds
> > extended burst = 2 * normal burst
> >
> > Aside from configured rate, where do the other parameters come from and
> what
> > are their respective meanings? I understand the classification and
marking
> > aspects of CAR, so there is no need for any explanation there. However,
a
> > practical example might help. For instance, lets say I have a 10mbit
> > Ethernet link and I've identified some flow that I want to constrain to
> 56k.
> > What would the policy-maps police statement look like?
> >
> > "police bps burst-normal burst-max conform-action action exceed-action
> > action violate-action action"
> >
> > police 56000 ????? ????? conform-action transmit exceed-action drop
> >
> > I'm runnung IOS 12.1(11)EA1 on a 3550 and get errors when I put in a
> normal
> > burst size under 8000bytes.
> >
> > SW1(config-pmap-c)#police 56000 ?
> > <8000-2000000> Normal burst bytes
> >
> > Also normal and extended burst are in bytes, while rate is in bits???
> >
> >
> > Thanks,
> >
> > Alsontra
> >
> > _______________________________________________________________________
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