From: Chris Lewis (chrlewiscsco@gmail.com)
Date: Wed Jan 11 2006 - 11:47:22 GMT-3
Nick,
A good post, but I think one point of detail may be lost here. I think the
point of detail is missed both in the original question and in the answer
provided. So I think the person that wrote the requirement was missing a
point of how priority-queue out works.
The priority-queue out command configures the 3550 to use strict priotity
scheduling for transmit queue 4. This means that any weighting assigned to
queue 4 by the wrr-queue bandwidth is meaningless, as if there is any
traffic in queue 4, it will be transmitted regardless of weighting
configured for that queue. In essence, when priority-queue out is
configured, the bandwidth allocation algorithm ignores weightings assigned
to queue 4. The documentation for the priority-queue out command states the
following:
"When you configure the *priority-queue out* command, the weighted round
robin (WRR) weight ratios are affected because there is one fewer queue
participating in WRR. This means that *weight4* in the *wrr-queue
bandwidth*interface configuration command 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. "
This is how it looks on a switch. I configure F0/1 as given.
interface FastEthernet0/1
switchport mode dynamic desirable
wrr-queue bandwidth 4 6 5 5
wrr-queue cos-map 1 6 7
wrr-queue cos-map 2 0 1 2
wrr-queue cos-map 3 4 5
wrr-queue cos-map 4 3
priority-queue out
end
Now I look at the following show command.
Switch#sho mls qos int f0/1 queueing
FastEthernet0/1
Egress expedite queue: ena
wrr bandwidth weights:
qid-weights
1 - 4
2 - 6
3 - 5
4 - 5 when expedite queue is disabled
Cos-queue map:
cos-qid
0 - 2
1 - 2
2 - 2
3 - 4
4 - 3
5 - 3
6 - 1
7 - 1
The important part to note is that queue 4 will have weighting 5 only if the
expedite queue is disabled.
What the configuration given means is that traffic in queue 4 will take
whatever it wants, then the remaining queues will have bandwidth allocated
as follows, as any weighting assigned to queue 4 when the priority-queue out
command is configured, is ignored:
Q1: 4/14 - (the figure 14 coming from the sum of weights fro queue 1, 2, 3)
Q2: 6/14
Q3: 5/15
Now if I take off the priority-queue command, all your math looks correct to
me, as verified by the output below:
Switch(config)#int f0/1
Switch(config-if)#no priority-queue out
Switch(config-if)#do sho mls qos int f0/1 que
FastEthernet0/1
Egress expedite queue: dis
wrr bandwidth weights:
qid-weights
1 - 4
2 - 6
3 - 5
4 - 5
Cos-queue map:
cos-qid
0 - 2
1 - 2
2 - 2
3 - 4
4 - 3
5 - 3
6 - 1
7 - 1
Chris
On 1/11/06, Nick <seajay76@nate.com> wrote:
>
> Please disregard the last strange mail.
>
> (1) With the priority-queue out, the 4th queue of the interface becomes
> the expedite queue.
>
> int fa0/4
> priority-queue out
>
> (2) you need to put the COS-3 packet int eh 4th queue
>
> int fa0/4
> wrr-queue cos-map 4 3 (they are the queue number and the CoS in order)
>
> (3) Then you can use the other remaining 3 queues.
>
> (4) Allocate the designated bandwidth to the queues.
>
> int fa0/4
> wrr-queue bandwidth 4 6 5 5
>
> Here 4 means 4/(4+6+5+5) , 6 means 6/(4+6+5+5) , 5 means 5/(4+6+5+5)
>
> So you might put it this way.
>
> int fa0/4
> wrr-queue bandwidth 20 30 25 25
>
> (5) Since you allocate the bandwidth to the queues,
> just put the CoSed packets in each queue
> You did it for the fourth queue already in (2)
>
> int fa0/4
> wrr-queue cos-map 1 6 7
> wrr-queue cos-map 2 0 1 2
> wrr-queue cos-map 3 4 5
>
> HTH~~
>
> Regards,
> Nick
>
> ----- Original Message -----
> From: <Bill.McKenzie@bisys.com>
> To: <ccielab@groupstudy.com>
> Sent: Wednesday, January 11, 2006 10:17 PM
> Subject: wrr-queue bandwidth command
>
>
> > Here is the requirement :
> > Cos-3 must be sent of everything else and match the following cos values
> to
> > according bandwidth.
> >
> > Cos 3 = 25%
> > CoS 6,7 = 20%
> > CoS 0,1,2 = 30%
> > CoS 4,5 = 25%
> >
> > Here is the solution:
> >
> > wrr-queue bandwidth 4 6 5 5
> > wrr-queue cos-map 1 6 7
> > wrr-queue cos-map 2 0 1 2
> > wrr-queue cos-map 3 4 5
> > wrr-queue cos-map 4 3
> > priority-queue out
> >
> >
> > I don't understand the values in the wrr-queue bandwidth command and
> trying
> > to look at the doc cd is just confusing me more. Can anyone point me to
> a
> > better explanation of how the values were estimated?
> >
> > Thanks,
> > Bill
> >
> >
> >
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