Saturday, May 16, 2009

srr-queue commands - part IV

The final part in my look at the srr queues is how DSCP or COS marked packets are assigned to the srr queues.

First the default settings

dscp default values 0-63

0-15 queue 2
16-31 queue 3
32-39, 48-63 queue 4
40-47 queue 1

cos default values 0-7
0,1 queue 2
2,3 queue 3
4,6,7 queue 4
5 queue 1

Within each queue marked packets can be placed in one of three threshold queues. By default all packets are placed in threshold 1. By default threshold 1 has the lowest tolerance to WTD.

The above default settings can all be adjusted depending on the requirements to be met with the following commands

mls qos srr-queue output dscp-map queue {queue-id} threshold {threshold id} {dscp1} ....{dscp8}
mls qos srr-queue output cos-map queue {queue-id} threshold {threshold id} {cos1} ....{cos8}

To ensure higher priority dscp or cos values are not dropped first they can be assigned to a threshold id with a higher value {2 or 3}. By default the higher threshold id values will have a higher tolerance to WTD.

Finally to review assignments use the show mls qos maps command.

Thats it for srr-queues. In my opinion, an absolute beast of a subject. Good to have an understanding of the configurable parameters, but the doc cd will be my friend should this come up.

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