From: Victor Cappuccio (vcappuccio@ccbootcamp.com)
Date: Tue Sep 04 2007 - 11:32:51 ART
Recommended Book for this
Tim Szigeti, CCIE No. 9794, Christina Hattingh
Copyright ) 2005 Cisco Systems, Inc.
Published by:
Cisco Press
800 East 96th Street
Indianapolis, IN 46240 USA
Excellent to have in the book self or in safari
Two-Rate Three-Color Marker/Policer
The single-rate three-color marker/policer was a significant improvement for
policers, in that it made allowance for temporary traffic bursts (as long as
the overall average transmitted rate was equal to or below the CIR). However,
the variation in the number of accumulated excess burst credits could cause a
degree of unpredictability in traffic flows. To improve on this, a two-rate
three-color marker/policer was defined in RFC 2698. This policer addresses the
peak information rate (PIR), which is unpredictable in the RFC 2697 model.
Furthermore, the two-rate three-color marker/policer allows for a sustainable
excess burst (negating the need to accumulate credits to accommodate temporary
bursts) and allows for different actions for the traffic exceeding the
different burst values.
The two-rate three-color marker/policer was introduced in Cisco IOS Software
Release 12.2(4)T and uses the following parameters to meter the traffic
stream:
PIR Peak information rate, the maximum rate that traffic ever is allowed
PBS Peak burst size, the maximum size of the first token bucket
CIR Committed information rate, the policed rate
CBS Committed burst size, the maximum size of the second token bucket
Tp Token count of CBS, the instantaneous number of tokens left in the PBS
bucket
Tc Token count of EBS, the instantaneous number of tokens left in the CBS
bucket
B Byte size of offered packet
The two-rate three-color policer also uses an algorithm with two token
buckets, but the logic varies slightly. Instead of transferring unused tokens
from one bucket to another, this policer has two separate buckets that are
filled each second with two separate token rates. The first bucket is filled
with the PIR number of tokens and the second bucket is filled with the CIR
number of tokens. In this model, the Be works the same as the Bc, except for
the PBS bucket (not the CBS bucket). This means that Be represents the peak
limit of traffic that can be sent during a subsecond interval.
The logic varies further in that the initial check is to see whether the
traffic is within the PIR. Only then is the traffic compared against the CIR.
(In other words, a violate condition is checked for first, then an exceed
condition, and finally a conform condition, which is the reverse of the logic
of the previous model.)
thanks,
Victor Cappuccio.-
- CCSI# 31452
CCBOOTCAMP - A Cisco Sponsored Organization (SO)
vcappuccio@ccbootcamp.com
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-----Original Message-----
From: Gregory Gombas [mailto:ggombas@gmail.com]
Sent: Tue 04-Sep-07 7:28 AM
To: Victor Cappuccio
Cc: groupstudy
Subject: Re: When to use PIR?
Thanks,
But how does that different from:
exceed action set-dscp
violate action set-dscp
?
On 9/4/07, Victor Cappuccio <vcappuccio@ccbootcamp.com> wrote:
> I found this Link very interesting about the topic
http://www.juniper.net/techpubs/software/junos/junos74/swconfig74-cos/html/co
s-tcm2.html#1196011
>
> With colorblind policing, all packets are evaluated by the CIR. If a packet
exceeds the CIR, it is evaluated by the PIR.
>
>
> thanks,
> Victor Cappuccio.-
> - CCSI# 31452
>
> CCBOOTCAMP - A Cisco Sponsored Organization (SO)
> vcappuccio@ccbootcamp.com
> Toll Free: 877-654-2243
> Direct: +1-702-968-5100 = Outside the USA
> FAX: +1-702-446-8012
> YES! We take Cisco Learning Credits!
> Training And Remote Racks: http://www.ccbootcamp.com
>
> Register to win a free iPhone! http://www.ccbootcamp.com/iphone.html
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com on behalf of Gregory Gombas
> Sent: Tue 04-Sep-07 6:54 AM
> To: groupstudy
> Subject: When to use PIR?
>
> Hey Folks,
>
> When configuring policing, when is it necessary to use PIR?
>
> From what I understand PIR allows you continuosly send traffic at a
> rate above your CIR (as opposed to occasional burst) but if that is
> that case, why not just set your CIR to that higher value?
>
> For example, if your CIR is 256k and PIR is 512k, the policer will
> allow you to send continously at 512k, correct? If that is the case,
> then why not just set your PIR to 512k?
>
> Thanks,
> Greg
>
> _______________________________________________________________________
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