01-19-2009 07:09 AM - edited 03-04-2019 12:53 AM
Hi<
Please can someone veify that by default you can only use 75% of available bandwidth of your physical interface, i mean 750M of 1G, otherwise you configure max-bandwith command to utilize 100%, but then it degrade the performance ?
Regards,
01-19-2009 07:26 AM
I configured some QoS the other day and used more than 75% of the bandwidth and got an error so I would say by default you can't. I would not say to use 100% I would say use as much as you need so as to not take any chances. I have actually changed one to 95% and there was no degrade in performance.
01-19-2009 07:34 AM
Thanks for the reply,
I would say it depend on packet size as well, wether its 64 or 1518.
The formula for Ethernet throughput is as follows:
- Frame rate (fps) = network speed ÷ ((frame size + 8 + 12) x 8)
- Data throughput (Mbps) = frame rate x frame size x 8
Data throughput is therefore dependent on packet size, where frame overhead has a bigger impact on smaller data loads.
With a 1518 packet size:
- Frame rate = (100 x 10e6) ÷ ((1,518 + 8 + 12) x 8) = 8,127 fps
- Data throughput = 8,127 Ã 1,518 Ã 8 = 98.69 Mbps
With a 64 packet size:
- Frame rate = (100 x 10E6) ÷ ((64 + 8 + 12) x 8) = 148,809 fps
- Data throughput = 148,809 Ã 64 Ã 8 = 76.19 Mbps
Regards,
01-19-2009 07:54 AM
Hi,
I'd rephrase your sentence:
You can only reserve 75% of available bandwidth to your CBWFQ classes with the bandwidth command by default leaving the 25% for the default class plus control plane protocols.
If you need to reserve more, you can use max-bandwith command to increase this limit.
But you should know very well the risk then.
BR,
Milan
01-19-2009 08:09 AM
As Milan correctly notes, on most platforms that support CBWFQ, you can define explicit class bandwidth reservations that sum up to 75% (unless the default is changed), however any class can still use 100% of the link (assuming it's not otherwise limited).
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