From: Brian McGahan (brian@cyscoexpert.com)
Date: Fri Feb 14 2003 - 19:10:51 GMT-3
George,
Yes there is a recommended formula.
normal burst = configured rate * (1 byte)/(8 bits) * 1.5 seconds
extended burst = 2 * normal burst
"Testing of TCP traffic suggests that the chosen normal and extended
burst values should be on the order of several seconds worth of traffic
at the configured average rate. That is, if the average rate is 10 Mbps,
then a normal burst size of 10 to 20 Mbps and an Excess Burst size of 20
to 40 Mbps would be appropriate.
We recommend 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
With the listed choices for parameters, extensive test results have
shown CAR to achieve the configured rate. If the burst values are too
low, then the achieved rate is often much lower than the configured
rate."
http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configur
ation_guide_chapter09186a00800bd8ed.html#1000977
HTH
Brian McGahan, CCIE #8593
Director of Design and Implementation
brian@cyscoexpert.com
CyscoExpert Corporation
Internetwork Consulting & Training
Toll Free: 866.CyscoXP
Fax: 847.674.2625
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Jerry
> Sent: Friday, February 14, 2003 3:43 PM
> To: george gittins; ccielab@groupstudy.com
> Subject: Re: question on rate limit
>
> George,
>
> I believe these limits are chosen by arbitrary policy based on
the
> type of traffic you are policing
>
> in the access list. I do not believe this comes from a formula. In
other
> words if you have as in your example a t-3 or ds-3 and you want no
more
> than
> 10 MEg for e-mail your access-list would match
> tcp port #25 and in the rate-limit statement you have the 10000000
> conform-action transmit exceed-action drop. I don't have exact syntax
> because I don't have any routers! But this should convey the
> general idea.
>
>
> Jerry
> ----- Original Message -----
> From: george gittins <g.gittins@edinburg.esc1.net>
> To: <ccielab@groupstudy.com>
> Sent: Friday, February 14, 2003 3:10 PM
> Subject: question on rate limit
>
>
> > I been reading up on Qos and I have somewhat difficult in grasping
the
> > following command.
> >
> > Rate limit . reading from the book and taking one example like
> >
> >
> >
> > Rate-limit input 450000 22500 22500 confirm-action
> >
> >
> >
> > Now I don't know how to calculate the 22500 value, or where it comes
> from.
> > On the book it explains that the link is a ds-3 and and the
objective
> is
> > to control that link not exceed , I understand that part and how to
> classify
> > it once the traffic arrives , its just the value of bps burst-normal
> > burst-max.is there a formula?
> >
> >
> >
> > rate-limit {input | output} [access-group [rate-limit] acl-index]
bps
> > burst-normal burst-max conform-action
> >
> >
> >
> >
> >
> > George Gittins
> >
> > Network and Computer Maintenance Supervisor
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