MAny thx Dave,

The thing I was wondering though, was not the wrr even though, man thx for letting me know that if the queue is empty, it is skipped, but it was a concern about the txq.

So, the default (what I beleive is the default) is as follows :- (lets pick a 2q2t)

Default Configuration

! 2q2t

set qos txq-ratio 2q2t 80 20

set qos wrr 2q2t 5 255

set qos drop-threshold 2q2t tx queue 1 80 100

set qos drop-threshold 2q2t tx queue 2 80 100

set qos map 2q2t tx 1 1 cos 0

set qos map 2q2t tx 1 1 cos 1

set qos map 2q2t tx 1 2 cos 2

set qos map 2q2t tx 1 2 cos 3

set qos map 2q2t tx 2 1 cos 4

set qos map 2q2t tx 2 1 cos 5

set qos map 2q2t tx 2 2 cos 6

set qos map 2q2t tx 2 2 cos 7

Cisco Recommendations in paper (http://www.cisco.com/application/pdf/en/us/guest/netsol/ns432/c649/ccmigration_09186a008049b062.pdf)

! 2q2t

set qos txq-ratio 2q2t 30 70

set qos wrr 2q2t 30 70

set qos drop-threshold 2q2t tx queue 1 40 100

set qos drop-threshold 2q2t tx queue 2 80 100

set qos map 2q2t tx 1 1 cos 1

set qos map 2q2t tx 1 2 cos 0

set qos map 2q2t tx 2 1 cos 2,3,4,6,7

set qos map 2q2t tx 2 2 cos 5

So in the first example, I am putting CoS 0,1,2,3 in Queue 1 and Queue 1 has a buffer allocation of the port of 80%.

The the second, CoS 0 and 1 go into Queue 1 with a buffer allocation of 30% of the port.

Now, if I run enable QoS on a large scale network, one would assume, this would be a major concern, or, if Queue 1 reaches it threshold of 30%, does it just tail drop or would it use buffers from queue 2?

Many thx,

Ken

Ken,

If the port is not over subscribed all traffic will go. If you have 80mb of traffic egressing a 100mb port it won't matter that 60mb is Q1 COS 0 which is only allocated 30%. If you have 150mb/s of traffic your mapping is going to determine what COS traffic will be dropped.

Here is a good doc on 6500 WRR:

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00801091a5.shtml

Dave

Hey fella :)

Again Thx. So let me make sure I got this right and am really sorry if I am being a dummy.

If i config the port txq-ratio using the command

set qos txq-ratio 2q2t 30 70

If i send 60 Mb of CoS 0 (no other traffic), it will all get sent? Also if I sent 90Mb it would get sent. If I send 110Mb 10Mb has to get dropped and that would use the drop threshold or would wrr determined the dropping of packets.

Or, are we saying from the document you sent, all 6500 ports use weighted tail drop as standard before any other congestion mechanisms take place? (The Catalyst 6000 has implemented an advanced version of tail drop congestion avoidance that drops all packets with a certain CoS when a certain percentage of buffer filling is reached. )

I am really really sorry, i am not getting this?

Kindest ragrds, and thx for the continued input,

Ken

I think I have this worded out now. Many thx for the help :))

One last point if I may,

Is RX queueing an important factor to consider, on switch-to-switch connections (not access) or just TX?

Many thx indeed,

Ken

Hi,

Normally you don't need to consider RX queueing because this will only come into play if the fabric is congested - an extremely unlikely scenario.

HTH

Andrew.

Many thx indeed,

Ken