From: Carlos G Mendioroz (tron@huapi.ba.ar)
Date: Fri Jun 04 2004 - 11:23:06 GMT-3
Me too. (inter class WFQ that is)
I've been told that there is sort of priority to bandwidth assigned
classes wrt non bandwidth assigned classes.
So if you have class a bw 10% and class-default w/o bw, enough class a
traffic can starve the rest of the link.
Bob Sinclair wrote:
> Guiherme,
>
> According to Wendell Odom in his book Cisco DQOS, the CBWFG algorithm is not
> published. I have a hard time seeing how it could be precedence-based, like
> WFQ. Do you have a reference you can share?
>
> Thanks!
>
> Bob Sinclair
> CCIE #10427, CISSP, MCSE
> www.netmasterclass.net
>
>
> ----- Original Message -----
> From: "Spolidoro, Guilherme" <Guilherme.Spolidoro@unisys.com>
> To: <ccielab@groupstudy.com>
> Sent: Friday, June 04, 2004 9:32 AM
> Subject: RE: QoS - Police - Congestion - NoCongestion
>
>
>
>>The word that should be used with CBWFQ is not reserve but guarantee.
>>
>>When you type the bandwidth percent 25 command on the class, what's gonna
>
> happen is that CBWFQ will guarantee at least 25% of the bw for this class
> during congestion.
>
>>If there's no congestion, the bw command will never kick off. It's used
>
> only during congestion, meaning it's basically a technology used to empty
> the queues (when used with the bw statement).
>
>>If there's enough bw for everyone, there's no reason to guarantee
>
> anything, right?
>
>>If this class doesn't need to use 25% or more (let's say it's using only
>
> 10%), the rest of the classes can use the remaining of the bw (the other 15%
> that this class doesn't need).
>
>>CBWFQ uses the WFQ algorithm, meaning that packets from the different
>
> classes that have the highest IP Precedence will be the ones to benefit more
> from that. Let me give you an example:
>
>>class a = streaming video (ip prec 4)
>>class b = bulk data (ip prec 1)
>>class c = voip (ip prec 5)
>>class default-class = anything else (ip prec 0)
>>
>>Class c has 25% of the bw guarantee for it, but might need only 10% at a
>
> given time.
>
>>Class a has 5% of the bw guarantee for it, but might need more than that
>
> at a given time.
>
>>Class b has 5% of the bw guarantee for it, but might need more than that
>
> at a given time.
>
>>class default-class has 25% of the bw guarantee for it by default, but
>
> might need more than that at a given time.
>
>>If there's congestion on the link, class c (voip) will get the 10% that it
>
> needs. Classes a, b and the default-class' overflow will compete for the
> remaining bandwidth. They will use at least the bw that is on the command
> plus whatever they can get.
>
>>Class a's overflow will be able to get more bw than class b and the
>
> default-class' overflows.
>
>>By the end, you might see something like this:
>>
>>Class c only needed 10% and that's what it got.
>>Class a ended up getting 35% of the total bw.
>>Class b ended up getting 25% of the total bw.
>>Class default-class ended up getting 30% of the total bw.
>>
>>Not sure if this is a good example, but the idea is that all the overflows
>
> will leave the queue faster or slower according to their IP Precedence...
>
>>Without making it more confusing than it has to be, there are other
>
> options on CBWFQ (besides the bw command):
>
>>- priority = new version of the low latency queue, typically used for voip
>
> or interactive video. Instead of putting the packets in the queue, it sends
> directly to the interface (except for the overflow) In our example, you
> could it on class c.
>
>>- policy = new version of the old CAR. Let you limit the traffic that the
>
> class can use either for inbound or outbound. I personally don't like it
> because the way it works (basically drops the excess) causes too many
> retransmissions.
>
>>- shape = new version of the old traffic shape. Let you limit the traffic
>
> that the class can use for outbound only. I use extensive here and it works
> very well.
>
>>I know this address a lot more than what you asked but I hope others on
>
> the list can benefit from it.
>
>>
>>-----Original Message-----
>>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
>>gladston@br.ibm.com
>>Sent: Friday, June 04, 2004 8:51 AM
>>To: ccielab@groupstudy.com
>>Subject: QoS - Police - Congestion - NoCongestion
>>
>>
>>Dear Group,
>>
>>Does Police within CBWFQ reserve a bandwidth when there is no congestion
>
> and when there is congestion?
>
>>For example, to reserve 25% of the bandwidth to traffic from 10.100.5.0 to
>
> 10.200.6.0:
>
>>Class-map p-100.5.0
>> Match access-group name p-100.5.0
>>!
>>policy QOS
>>class p-100.5.0
>>police 10000 1000 conform-action transmit exceed-action drop
>>!
>>interface ser 1
>> service-policy output QOS
>>
>>
>>If so, why should one use bandwidth and policy within the same class?
>>
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>
>
> _______________________________________________________________________
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-- Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
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