QoS - Cisco Best Pratice - Wastage of Port capacity

Unanswered Question
Jan 22nd, 2008

So,

Let say you do have 8 classes of traffic and you implement Cisco best practices for QoS for a 1p3q8t port as follows :-

set qos enable

set qos map 1p3q8t tx 2 1 cos 0

set qos map 1p3q8t tx 1 1 cos 1

set qos map 1p3q8t tx 3 2 cos 2

set qos map 1p3q8t tx 3 3 cos 3

set qos map 1p3q8t tx 3 1 cos 4

set qos map 1p3q8t tx 3 4 cos 6

set qos map 1p3q8t tx 3 5 cos 7

set qos wrr 1p3q8t 5 25 70

set qos txq-ratio 1p3q8t 5 25 40 30

set qos wred 1p3q8t tx queue 1 80:100 100:100 100:100 100:100 100:100 100:100 100:100 100:100

set qos wred 1p3q8t tx queue 2 80:100 100:100 100:100 100:100 100:100 100:100 100:100 100:100

set qos wred 1p3q8t tx queue 3 50:60 60:70 70:80 80:90 90:100 100:100 100:100 100:100

set qos cos-dscp-map 0 8 16 24 34 46 48 56

If you only have voice and best efforts data, ie EF (46) and BE (0), plus your control traffic, (ie, CS6 and CS7 for routing stuff), would it not be worth doing the following :

set qos enable

set qos map 1p3q8t tx 1 1 cos 0

set qos map 1p3q8t tx 1 1 cos 1

set qos map 1p3q8t tx 1 1 cos 2

set qos map 1p3q8t tx 1 1 cos 3

set qos map 1p3q8t tx 1 1 cos 4

set qos map 1p3q8t tx 1 2 cos 6

set qos map 1p3q8t tx 1 2 cos 7

set qos wrr 1p3q8t 70 0 0

set qos txq-ratio 1p3q8t 70 0 0 30

set qos wred 1p3q8t tx queue 1 80:100 100:100 100:100 100:100 100:100 100:100 100:100 100:100

set qos wred 1p3q8t tx queue 2 100:100 100:100 100:100 100:100 100:100 100:100 100:100 100:100

set qos wred 1p3q8t tx queue 3 100:100 100:100 100:100 100:100 100:100 100:100 100:100 100:100

set qos cos-dscp-map 0 8 16 24 34 46 48 56

??????????

So just use Q1 for all your traffic, and set the wred threshold to 2 for CS6 and CS6? With voice going into the SP Queue.

Ot is there a better config for networks that just have Voice and best efforts data?

I suppose you could just set another threshold for call signalling and tweak the CS3 stuff in there also?

"THE POINT"

It seems like I am reserving with the txq-ratio, 40% of the entire port buffer for queue 3 and reserving 5% for scavenger and then also this is getting 70% and 5% of the scheduling which I assume will not matter if there is no traffic in the queue to be scheduled?

Could someone please help me with this :)) Is the Cisco Best Practice config (the first one) wasteful for this type of traffic profile (two classes - voice and data best efforts)?

Many thx indeed,

Ken

I have this problem too.
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Ken,

If I were the one configuring the network then I would wouldn't setup the custom queues and cos mappings. This will ensure an easier network manage and takes into account a learning curve for anyone who may configure the network in the future.

As to your question about is the Cisco config wasteful I would say no. The beauty of the QoS design is not in default queue mappings but in the classes/policies that you create and apply. Cisco best practice is to not touch the queue config and use EF for voice and cs0 for non priority traffic. Those are taken care of in the classes/policie an not in the queue config.

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