What does QOS use as a reference?

Does QOS on an interface take into account the line speed, or does it use the bandwidth configured on an interface much like a routing protocol would?

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Comments

joetest

Remember regarding EIGRP metric changes - most commonly using delay, bandwidth or offset-lists.

One of them is not really recommended because it has an effect other things.. like QoS or other routing protocols

james43026

Thanks joetest. I also found lots of other unofficial documentation saying that the interface bandwidth is what is used. I also found this

[h=2]bandwidth qos-reference[/h]To configure bandwidth to be used as a reference for calculating rates of quality of service (QoS) percent configurations on a physical or logical interface, use the bandwidth qos-reference command in interface configuration or subinterface configuration mode. To remove this explicitly specified reference bandwidth, use the no form of this command.
bandwidth qos-reference bandwidth-amount
no bandwidth qos-reference bandwidth-amount

Seems like a pretty usefull command if you wanted to make an impact on QOS without disturbing other protocols or processes.

james43026

On the subject of QOS, exactly what happens if you were to assign two QOS policies to an interface. And lets say they were both using the bandwidth command, so as to allow a minimum bandwidth allocated, and they were both configured to use the full bandwidth of the interface as their minimum. Would the first policy to take up bandwidth be the one that gets to keep the bandwidth until it no longer needs it?

networker050184

It won't allow you to apply two to the same interface.

james43026

Ahh okay. Thanks for the response. I'll have to fire up the home lab and play around with QOS some more, to get to know the intricacies a bit more. I have a few other questions that I think would be worth labbing to find out for myself.

DCD

Any good labs for QOS out there?

james43026

I think GNS3 vault may have a few. And the youtube channel routergods has a series of videos on QOS configs.

DCD

Thanks, I did find those.

james43026

networker050184 wrote: »

It won't allow you to apply two to the same interface.

What if you allocate multiple classes to the same policy-map, and the cumulative minimum bandwidth of the classes exceed the bandwidth of the interface that it is applied to? In this scenario we would be using the bandwidth command to set the minimum bandwidth. Since we are using bandwidth we would obviously start queuing traffic. I'll take it that the router would then just use WFQ to drop traffic from the queues?

networker050184

Exactlty how it operates depends on your platform and ios (hqf or not mostly and your reserved bandwidth), but it won't let you do that either.