3550 QOS : WRR

On 3550 : Weighted Round Robin is done per packet
On 6000/6500 : Weighted Round Robin is done by bandwidth

wrr-queue bandwidth 10 20 30 40

On gigabit ports:

The 4 queues could be assigned a different amount of buffer size and WRED or RED with 2 thershold by queues :

Wred :
wrr-queue random-detect max-threshold 1 50 100

Red :
wrr-queue threshold 1 50 100

Queue Size:
wrr-queue queue-limit Q_size1 Q_size2 Q_size3 Q_size4

On non-gigabit ports:

Only FiFO with a reserved number of packet by queues, (max 170) :

mls qos min-reserve level buffer_size
wrr-queue min-reserve level queue

3560 QOS

Differents tasks that could be asked :

1 Map Ingress DSCP value to different queues and WTD :

There is 2 input queues each with 2 different WTD threshold

Followinbg example maps dspc 00 and 01 to the queue 1 threshold 2 and configure for queue 1 and threshold 1 of 75 and threshold 2 of 50 and for queue 2 a threshold1 of 30 and a threshold 2 of 75

mls qos srr-queue input dscp-map queue 1 threshold 2 00 01
mls qos srr-queue input threshold 1 75 50
mls qos srr-queue input threshold 2 30 75


2 Configure the ingress bandwidth association to queues

Here 20 % is dedicated to Expedite queue 2, the remain bandwidth is shared between queue 1 35% and queue 2 45%

mls qos srr-queue input bandwidth 35 45
mls qos srr-queeu input priority 2 bandwidth 20

3 Modifiy default buffer

Buffer is the amount of packet each queue could contains before dropping

Input buffer is globally modified with :
mls qos srr-queue input buffer 60 40

Ouput is modified by Queue-set. Queue-set 1 is by default applied to all interfaces with egal shared. To apply a different queue-set to an interface :

mls qos queue-set output 2 buffers 40 20 20 20
int fa0/14
queue-set 2

4 Configure bandwidth shaping and sharing on interface

Shaped queue limit the bandwidth, whereas shared only limit during congestion.
Shape weight is an inverse ration 1/weight
Share weight is a ration weight_queue1/total_weight
0 in shape means queue is treated as shared. The remain bandwith is for shared.
A queue in shape mode is not take into account on the shared ratio.

Example Queue 1 is a shared queue with 12,5 percent of the bandwidh, the remaining bandwidth is shared among q2, q3, q4.

srr-queue bandwidth shape 8 0 0 0
srr-queue bandwidth share 25 25 25 25