cisco router dynamic QoS

joshorenberg · ‎04-20-2012

Hello I live in a condo building that uses 3 Cisco Catalyst 3550 switches connected to a Comcast router with 100 Mbps download. Currently we regulate bandwidth by providing each user with 3 Mbps download using bandwidth policing on the switches. Even if only two people are active they still only get 3 Mbps download. I would like to set it up so if two people are using they each get 50 Mbps and if four they each get 25 etc.; a sort of 'dynamic qos.' I called Cisco and they recommended the 881-k9 router for our setup to provide dynamic bandwidth regulation. They said it could handle up to 300 users. We have 100 units in the condo building and about 50-75 units using the building Internet. Does anyone disagree with these claims? Have any information that is relevant? Thanks so much for your time and help!

-Josh

Joseph W. Doherty · ‎04-20-2012

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Posting

I disagree.

First, I believe the 881 might struggle with 100 Mbps. Where your 3550s "yawn" dealing with 100 Mbps, many of the smaller software based routers are designed for much lower WAN bandwidths.

Second, managing bandwidth, as you desire/describe, downstream of the choke point isn't possible on a router (at least not that I'm aware of). If you were on the upstream end, FQ per flow would do the trick. Downstream a bandwidth managing appliance might be able to do this.

PS:

You could shape your egress to use less than 100 Mbps and FQ per flow that - as it would become the new choke point, it would work as you describe/desire. Besides losing whatever bandwidth you shape down to, effectiveness decreases at you near your full bandwidth. E.g. shape for 10 Mbps, probably would work very well, shape for 99 Mbps probably ineffective.

joshorenberg · ‎04-20-2012

Can you describe in less technical terms the second and third paragraphs?

Joseph W. Doherty · ‎04-20-2012

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Choke point = least amount of bandwidth (Comcast can has more than 100 Mbps and I assume your switch have multiple ports, so the choke point or bottleneck is the 100 Mbps total download bandwidth)

Downstream = on the receiving end

FQ = fair-queue (each active flow gets equal share to bandwidth)

Bandwidth managing appliance = e.g. Packeteer

Shape = send at a slower (average) rate than an interface actually can transmit at

Egress (from you device - 3rd paragraph = from Comcast to your clients)

Comcast Modem - to your device at 100 Mbps - if your device shapes, with FQ, at (for example) 60 Mbps to your clients then :

One client could obtain 60 Mbps; two clients would have a guarantee of 30 Mbps each, but if one was only using 20 other could use the 40; three clients would each have guarantee of 20 Mbps each, but one or two could use bandwidth not being used by the other(s).