From: James R. Yeo (james@net-brigade.com)
Date: Fri Jul 16 2004 - 11:03:17 GMT-3
Have a look @ this:
Configuring the Egress Expedite Queue
You can ensure that certain packets have priority over all others by
queuing them in the egress expedite queue. WRR services this queue until
it is empty before servicing the other queues.
Beginning in privileged EXEC mode, follow these steps to enable the egress
expedite queue:
Command Purpose
Step 1 configure terminal
Enter global configuration mode.
Step 2 mls qos
Enable QoS on the switch.
Step 3 interface interface-id
Enter interface configuration mode, and specify the egress Gigabit-
capable Ethernet interface.
Step 4 priority-queue out
Enable the egress expedite queue, which is disabled by default.
When you configure this command, the WRR weight and queue size ratios are
affected because there is one fewer queue participating in WRR. This means
that weight4 in the wrr-queue bandwidth command is ignored (not used in
the ratio calculation).
Step 5 end
Return to privileged EXEC mode.
Step 6 show running-config
Verify your entries.
Step 7 copy running-config startup-config
(Optional) Save your entries in the configuration file.
To disable the egress expedite queue, use the no priority-queue out
interface configuration command.
Allocating Bandwidth among Egress Queues
You need to specify how much of the available bandwidth is allocated to
each queue. The ratio of the weights is the ratio of frequency in which
the WRR scheduler dequeues packets from each queue.
Beginning in privileged EXEC mode, follow these steps to allocate
bandwidth to each queue:
Command Purpose
Step 1 configure terminal
Enter global configuration mode.
Step 2 mls qos
Enable QoS on the switch.
Step 3 interface interface-id
Enter interface configuration mode, and specify the egress Gigabit-
capable Ethernet interface.
Step 4 wrr-queue bandwidth weight1 weight2 weight3 weight4
Assign WRR weights to the egress queues.
By default, all the weights are set to 25 (1/4 of the bandwidth is
allocated to each queue).
For weight1 weight2 weight3 weight4, enter the ratio, which determines the
ratio of the frequency in which the WRR scheduler dequeues packets.
Separate each value with a space. The range is 1 to 65536.
All four queues participate in the WRR unless the expedite queue (queue 4)
is enabled, in which case weight4 is ignored (not used in the ratio
calculation). The expedite queue is a priority queue, and it is serviced
until empty before the other queues are serviced.
A weight of 1 means that the minimum bandwidth is allocated for that
queue.
To allocate no bandwidth for a queue, use the wrr-queue cos-map interface
configuration command so that the available bandwidth is shared among the
remaining queues.
Step 5 end
Return to privileged EXEC mode.
Step 6 show mls qos interface queueing
Verify your entries.
Step 7 copy running-config startup-config
(Optional) Save your entries in the configuration file.
This example shows how to configure the weight ratio of the WRR scheduler
running on the egress queues. In this example, four queues are used (no
expedite queue), and the ratio of the bandwidth allocated for each queue
is 1/(1+2+3+4), 2/(1+2+3+4), 3/(1+2+3+4), and 4/(1+2+3+4), which is 1/10,
1/5, 3/10, and 2/5 for queues 1, 2, 3, and 4.
Switch(config)# interface gigabitethernet0/1
Switch(config-if)# wrr-queue bandwidth 1 2 3 4
On Fri, 16 Jul 2004 09:51:10 -0400, gladston@br.ibm.com wrote :
> Suppose we should reserve 35% of the bandwidth for queue 3 on 3550. The
system acepts the command wrr-queue bandwidth 22 22 35 22. The sum of
these numbers give us 106. Even though the system acept the command, it
seems it has a decision to make: which queue will receive less bandwidth,
because I can not give 22% for queue 1, 22% for queue2, 35% for queue 3
and 22% for queue 4. Is that correct? or it just represent a time and is
not limited to 100%?
>
> "...determines the ratio...in which the WRR scheduler dequeues packets".
> Can I conclude that if there is congestion 35% will be reserved to queue
3 and if there is no congestion queue 3 can use more than 35%?
>
> S1#c
> Enter configuration commands, one per line. End with CNTL/Z.
> S1(config)#int fa 0/2
> S1(config-if)#wrr-queue bandwidth 22 22 35 22
>
>
> S1#sh mls qos interface fa 0/2 queu
> FastEthernet0/2
> Egress expedite queue: dis
> wrr bandwidth weights:
> qid-weights
> 1 - 22
> 2 - 22
> 3 - 35
> 4 - 22
>
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