From: Matt Holbert (mholbert@xxxxxxxxxxx)
Date: Sun Feb 10 2002 - 23:21:36 GMT-3
WFQ is a congestion management technique, while WRED is a congestion
avoidance technique. So, they can both be configured on the same interface.
Special rules apply when you define classes of traffic and apply these
techniques.
Within a class-map, the bandwidth command is required before random-detect
can be configured, unless it is the default class-map. The class-default
with random-detect requires either fair-queue or bandwidth. If you want to
do WRED without CBWFQ within a policy-map, use only the class-default.
Wouldn't be too practical (you could do it with fewer commands on the major
interface), but that's how to do it.
Side comment about the book: I have not read the book. But I do know that
Cisco sometimes changes the configuration format for QoS between revisions.
And, the IOS is littered with bugs. So, I'm not surprised that the book may
need to be revised to clarify the examples.
Matt Holbert
-----Original Message-----
From: Jon Carmichael [mailto:jonc@pacbell.net]
Sent: Sunday, February 10, 2002 2:39 PM
To: Bill Greenwood; ccielab@groupstudy.com
Subject: RE: Playing with WRED
That's it!
Thanks Bill, that was exactly what I was looking for.
Someone asked me what I thot of the book "IP Quality of Service" and I must
say that his explanations vary from being clear and sometimes not so clear,
but the examples of syntax suck! He spends an appropriate amount of time
explaining the differences between CPU based queuing verses VIP based
queuing, however his IOS syntax is sometimes incomplete or difficult to
reproduce.
But it is a comprehensive coverage of the subject, I just think it already
needs a second edition with better examples.
JONC
-----Original Message-----
From: Bill Greenwood [mailto:billgreenwood@earthlink.net]
Sent: Sunday, February 10, 2002 9:26 AM
To: Jon Carmichael; ccielab@groupstudy.com
Subject: Re: Playing with WRED
When you configure the interface enter the "randon-detect" on the interface.
This will enable RED, then enter the "randon detect" again with the question
mark (randon-detect ?) and you will see that you now can enter the rest of
the commands for WRED.
----- Original Message -----
From: "Jon Carmichael" <jonc@pacbell.net>
To: <ccielab@groupstudy.com>
Sent: Sunday, February 10, 2002 1:43 AM
Subject: Playing with WRED
> I'm having lots of fun here trying to make WRED work. Following the book
IP
> Quality of Service, by Srinivas Vegesna for those of you who might have
the
> book or are interested in making this work. I'm struggling with the
> relationship between WRED and CBWFQ, and why I'm being forced by the IOS
to
> treat those two as the same, perhaps WRED is a subset of CBWFQ?
>
> I'm working an example similar to his on page 134, but not getting the
> results I would like. I've done this on a 2500 and a 4500 with the same
> result, and that is that it keeps thinking that I'm doing CBWFQ, when I
want
> to make WRED drop some packets. I'm setting my minimum-threshold to 2, my
> maximim threshold to 4 for all precedence levels, where I think I can
> generate enough tcp packets so force some drops, but the problem is that
my
> interfaces think it's CBWFQ as soon as I put a service-policy on them,
when
> what I thot I wanted is WRED.
>
> Of course RED, is not WRED, and if you do "random-detect" on the
interface,
> you don't get to mess with weights, but a service-policy, to follow the
> example in the book is coming up as CBWFQ. Even after I put
"random-detect"
> in my policy-map, I am still required to put a "bandwidth" before I can
set
> things like the "exponential-weighting-constant" or the "random-detect
> precedence..." Of course once I apply the policy-map to the interface
it
> pops up with a queueing strategy of CBWFQ, where I was hoping to see WRED.
>
> The relevant parts of my configuration are below..
>
> * * *
> class-map non-critical
> match access-group 101
> !
> !
> policy-map SET-WRED
> class non-critical
> bandwidth 8
> random-detect
> random-detect exponential-weighting-constant 3
> random-detect precedence 0 2 4 1
> random-detect precedence 1 2 4 1
> random-detect precedence 2 2 4 1
> random-detect precedence 3 2 4 1
> random-detect precedence 4 2 4 1
> random-detect precedence 5 2 4 1
> random-detect precedence 6 2 4 1
> random-detect precedence 7 2 4 1
> !
> * * *
>
>
> JONC
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