Re: Catalyst QoS srr-queue - wrr-queue

I can give you what I have figured reasoned,,,because I am exactly where you
are.

Each interface has a "magic number" of buffers assigned for egress and
ingress.
The magic number is some compilation of the small buffers, big buffer, very
small etc ( show buffers ).

This magic number of buffers can be divided between the 4 egress Queues and
2 ingress queues.
The buffers are divide by weights.
When you show command:

show mls qos queue-set 1

SW2#sh mls qos queue-set 1
Queueset: 1
Queue : 1 2 3 4
----------------------------------------------
buffers : 25 25 25 25
threshold1: 100 200 100 100
threshold2: 100 200 100 100
reserved : 50 50 50 50
maximum : 400 400 400 400

The buffers number in this output are the percent of available buffers
assigned to egress interfaces for interfaces belonging to queue-set 1.
So, of the magic number of buffers, 25% are assigned to each queue.

Threshold 1 shows 100 for all 4 queues.
This means...of the 25% of the buffers assign to queue 1, threshold 1 can
use all 100% of the buffers assigned to Q1 if needed.
Same for Threshold 2.

Reserved for Q1 means that of the 25% buffers assigned to Q1, Q1 will keep
50% for them "reserved or locked" and will not let any other queue borrow
them.
But the remaining 50% that was assigned to Q1 are put into a queue pool for
the other queues to borrow.

Maximum 400 for Q1 means that Q1 is allowed to use up to 400% or 4 times
his allotted buffers by borrowing from the buffer pool.

In a CCIE scenerio, I would think that if they wanted you to do anything
with buffers, they will just tell you what to set the buffers, thresholds,
reserve and weight to. Something like...for Q1 queue-set 2, set buffer
weight: 35, threshold 1: 130% threshold 2: 128%, reserved: 41%, Maximum: 389
leave all other queues default. Then, assign que-set 2 to interface fa0/4.
 Or, something like that..

I hope this helps

Chris

On Sun, Aug 15, 2010 at 1:34 AM, Gary Duncanson <
garyduncanson_at_btinternet.com> wrote:

> Group,
>
> Has anyone got any links that explain in a sane way how the
> weights/thresholds
> work on Catalysts? Other than that I have QoS down I think but defining
> these
> things to meet a requirement remains a singularly mysterious task.
>
> Cheers
> Gary
>
>
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Received on Sun Aug 15 2010 - 02:23:13 ART