From: Wes Smith (wesmith@rogers.com)
Date: Tue Mar 23 2004 - 20:38:55 GMT-3
Do you need shaping .? .. Maybe. Idealy yes, but maybe not.
Many people don't shape Lan Extensions, because it's been hard to do
without putting a router inplace.
It all depdends on if you want qos (voice) over that link and on how
much burst they have in that policer.
If they have configured a small burst l, then it'll react very quickly,
and drop packets to soon.
TCP flows will see this as congestion, and back off their windows.
Thruput will drop like a stone. If they have a reasonable burst size,
maybe it'll be ok.
But Try it. If you can get close to 3 meg thru it, and you don't need
qos .. then you won't need a shaper.
As for the 3550. I'm not aware of many switches that do shaping.
Lots of routers and smaller machines, perhaps even the Netscreen do
shaping at 10Meg or less.
Not many do it for fast/GigE . Shaping requires a lot of memory as it
implies buffering of data.
At FastE and gig speeds ... that's a awful lot of data for a shaper....
or a small shaper queue depth ..which sort of defeats the purpose.
3570Metro was the first 'lower end' box I've seen... but I'm pretty
cisco oriented. There may be others out there
All the new switches seem to have it.
btw .. the IPERF tool at http://dast.nlanr.net/Projects/Iperf/ is a
great tool for testing this type of thing.
You can set the windows size ... etc.
Wes
Richard Dumoulin wrote:
>So am I right in thinking that there is a problem here ? And that it is a
>pain that the 3550 is not able to shape ?
>
>Luckily there is a Netscreen in between and if I remember well it is able to
>shape,
>
>Thank you for your reply,
>
>--Richard
>
>-----Mensaje original-----
>De: Wes Smith [mailto:wesmith@rogers.com]
>Enviado el: martes, 23 de marzo de 2004 14:57
>Para: Richard Dumoulin
>CC: ccielab@groupstudy.com
>Asunto: Re: Traffic shaping on Cat3550
>
>
>We had a very similar situation last year.
>You're correct... 3550 only polices. But at least it polices output,
>which a Cat6K Sup1/Sup2 can't do.
>
>At that time ... you were limited to (with cisco gear) the following
>devices that could shape.
>- An IOS Router
>- Cat4K with Sup IV
>- Cat6K with Sup720 (with the new line cards)
>- Cat6K/7600with OSM line card (Big $$$$$)
>- You can now look at the new 3750 Metro switch.. It's probably their
>most affordable high speed shaper
>
>For 4 Mbs you could use a regular router. A 2621XM might be big
>enough ..
>2951/2691/3700 would be better. We tested 7301s shaping up to 150Mbs
>with out problems.
>Wes
>
>Richard Dumoulin wrote:
>
>
>
>>Hello group,
>>
>>
>> Suppose we have a cat 3550 configured as a L3 switch connected to an ISP.
>>The connection is at 100Mbps but the provider is rate limiting at 4 Mbps. I
>>suppose the ISP is dropping all the traffic bursting beyond 4 Mbps. Also I
>>suppose it is very easy to burst beyond 4 M if the link is configured at
>>
>>
>100
>
>
>>M ?
>>
>>What could you suggest as a solution. I would like Traffic Shaping but with
>>Cat3550 it's only possible to do Traffic Policing no ?
>>
>>Thanks,
>>
>>Richard Dumoulin
>>
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