From: Filyurin, Yan (yan.filyurin@eds.com)
Date: Sun Jul 22 2007 - 19:56:34 ART
Thank you and that does help. Where I was getting confused is thinking
that CAR is like CBQ and has typical two buckets and violate action,
which is always to drop. which it doesn't. It looks like that the token
bucket is the size of burst size and as soon as it does not have enough
tokens, traffic exceeds, but if there is excess burst size it has some
chance of conforming, but once it crosses that threshold it always
exceeds.
So I guess the original two statements are mentioned would not be equal.
I always found two pretty good URLs that explains it even more.
http://www.cisco.com/warp/public/732/Tech/car/
http://www.cisco.com/warp/public/105/cbpcar.html
"
Arriving packets which fail to conform to the token bucket specification
(either because they exceed the excess burst limit or because they fell
between the normal burst limit and the excess burst limit and were
probabilistically discarded) are handled via the specified exceed
action.
"
This part helped.
And thank you for responses.
Yan
________________________________
From: petrsoft@gmail.com [mailto:petrsoft@gmail.com] On Behalf Of Petr
Lapukhov
Sent: Sunday, July 22, 2007 4:37 AM
To: Filyurin, Yan
Subject: Re: CAR vs. Class Based Policing
Hi,
check out this link:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cg/hq
os_c/part20/qchpolsh.htm#wp1000944
Although CAR uses "two" buckets, it is not "RFC-Compliant" in the sense
of marking/coloring behavior.
Basically, the main difference is that Be is used to implement a
RED-like dropping behavior when
bursts fall in between Bc and Be (not like "second averaging interval"
with MQC policer)
<DocCD>
Rate limits define which packets conform to or exceed the defined rate
based on the following three parameters:
* <http://www.cisco.com/univercd/illus/images/blank.gif> Average rate.
The average rate determines the long-term average transmission rate.
Traffic that falls under this rate will always conform.
* <http://www.cisco.com/univercd/illus/images/blank.gif> Normal burst
size. The normal burst size determines how large traffic bursts can be
before some traffic exceeds the rate limit.
* <http://www.cisco.com/univercd/illus/images/blank.gif> Excess burst
size. The excess burst (Be) size determines how large traffic bursts can
be before all traffic exceeds the rate limit. Traffic that _falls
between the normal burst size and the excess burst size_ exceeds
the rate limit with a probability that increases as the burst size
increases.
The maximum number of tokens that a bucket can contain is determined by
the normal burst size configured for the token bucket.
When the CAR rate limit is applied to a packet, CAR removes from the
bucket tokens that are equivalent in number to the byte size of the
packet. If a packet arrives and the byte size of the packet is greater
than the number of tokens available in the standard token bucket,
extended burst capability is engaged if it is configured.
</DocCD>
-- Petr Lapukhov, CCIE #16379 (R&S/Security/SP) petr@internetworkexpert.comInternetwork Expert, Inc. http://www.InternetworkExpert.com
2007/7/22, Filyurin, Yan <yan.filyurin@eds.com>:
Hello Group Study. Could you help me understand or point me to a good URL on all the differences and distinction between CAR and Class Based Policing. Mainly I am wondering what exceed action will do. For example, if I were to do:
Class class-default (on inbound policy map) Police 8000 2000 2000 conform-action transmit exceed-action set-dscp-transmit 0 violate-action drop
Or
Rate-limit input 8000 2000 4000 conform-action transmit exceed-action set-dscp-transmit 0
In other words, if the parameters are defined this way is exceeding action pretty much identical in this case and once in case of CAR it goes beyond the exceed action boundary it would get dropped, as if I were to set the violate action to drop?
Thank you
Yan
This archive was generated by hypermail 2.1.4 : Sat Aug 18 2007 - 08:17:41 ART
