From: asadovnikov (asadovnikov@comcast.net)
Date: Tue Dec 09 2003 - 03:15:49 GMT-3
Ken,
If you use "set-prec-continue" for exeed-action of the first statement then
the excess traffic which originally had precedence 1 would be marked down to
precedence 0 and then rate limited alone with all other traffic to 100000 by
the second CAR entry. This option employs cascading policing when traffic
which was not deemed conforming to first policer is marked down and then
policed again alone with other traffic by the second policer.
If you use "set-prec-transmit" for exeed-action of the first statement then
the excess traffic which originally had precedence 1 would be marked down to
precedence 0 and then transmitted without extra rate limiting. In this
option 2 policers are independent and traffic once considered by the first
policer will not be considered by the second one.
My reading of the desired rate limiting is that the "set-prec-transmit", but
I find that the objective is phrased loosely enough so either solution can
be argued for.
The CAR operates of token bucket, with average rate defined by first number
in the command. An intention is for traffic below average rate to conform
and above to exeed. How exactly traffic conforms/exceeds is defined by
normal and excess burst, which describe how high traffic can burst. Traffic
within normal burst conforms, and traffic between normal and excess burst
may conform or exeed with probability increasing with the actual burst size.
This functionality is intended for TCP traffic and deploys WRED like drop
behavior.
I find the burst parameters in your example a little to large, an example of
recommended configuration is:
configured rate = 20000 bits per second, then
normal burst = configured rate * (1 byte)/(8 bits) * 1.5 seconds = 3750
bytes
extended burst = 2 * normal burst = 7500 bytes
The above is way simplified description of how CAR works. Unfortunately
fine details of CAR operation are somewhat complex, but the CD DOCs
description is very good:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos
_c/fqcprt4/qcfpolsh.htm#1000977
Best regards,
Alexei
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Ken.Farrington@barclayscapital.com
Sent: Monday, December 08, 2003 2:21 PM
To: ccielab@groupstudy.com
Subject: CAR "Ball Breaker"
Guys, excellent car page on http://www.opalsoft.net/qos/WhyQos-2425.htm
qeustion i have thopught of from reading this,
rate limit out traffic to 20k/40k/60k (bw/bur/exbur) for all priority
(prec1) traffic, if exceed should be prec 0 (normal)
Also all other traffic rate limit out to 100k/120k/140k
on the first CAR statement, I am not sure if I use set-prec-continue or
set-prec-transmit ?
also, when is the exceed limit actioned, on the BW/Burst/ExBurst?
Hope this does not sound too stupid a question??????
int e0/0
rate-limit out access-group 121 20000 40000 60000 conform-action transmit
exceed-action set-prec-continue 0
rate-limit out access-group 122 100000 1200000 1400000 conform-action
transmit exceed-action drop
!
access-list 121 permit ip any any prec 1
access-list 122 permit ip any any
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