From: steve mou (router.mou@gmail.com)
Date: Wed Dec 27 2006 - 07:38:59 ART
Hi,
After reading the 3560 configuration guide, please let me explain to you.
1. for the second commad there is fine tuning in queue 2 i don't
understand deeply the configured values for drop threshold 1 and drop
threshold 2 ( 40 & 60) and I don't understand what they are
configured for.
for drop threshold 1 and drop threshold 2 (40 & 60), these are values
configured for WTD, different cos or dscp value can be assigned to
either threshold 1 or threshold 2
with the command:
mls qos srr-queue output dscp-map queue queue-id threshold 1/2 dscp1...dscp8
packets with assigned cos / dscp value will be droped accordingly.
2. the other two values I think they are as follow: 100 is the guaranteed
> memory for the queue, it means the queue will ot put any excess
> buffers to the allocated pools
>
> and value 200 means that the queue can borrow double the the allocated
> buffers---. ( 160x2) in case there is congetion, more than that it
> will drop packets and I have another question here does 200 percent
> means it will bowwo 160x2 buffers or will borrow only 160 additional
100% is the reserved buffer, and 200% is the maximum buffer for the
queue. switch 3560 provide two sets of buffer memory pool for egress
interface: reserved pool and common pool. reserved pool is mean for
guranteed memory for individual egree queue, and common pool will be
shared among the egree queues.
in command
Switch(config)# mls qos queue-set output 2 buffers 40 20 20 20
queues are located with different percent of buffers, and the sum of
the buffers are the size of the reserved pool.
that is: 40% of the reserved pool memory gives to queue 1 and so on...
so in the command
Switch(config)# mls qos queue-set output 2 threshold 2 40 60 100 200
40 60 100 200, are referring to the percentage of located buffers to
the queue .
queue 2 will take up 100% of the reserved pool, if change 100 to 70,
queue will only take up 70% of its located reserved pool, the rest 30%
of the reserved pool will contribute to common pool.
now, for the 200%, the queue 2 will try to borrow the rest (200 - 100)
% from the common pool iff there are still enough buffer memories left
in the common pool, in another word, the extra 100% of buffer memory
is not gurranteed, all depending on the usage of the common pool.
If any of my explaination is wrong, please corret me.
For detailed explaination, you can read cisco's 3560 configuration
guild under the confgure qos section.
Regards
Steve
On 12/27/06, david robin <robindavi@gmail.com> wrote:
> Dear ALl,
> I cant understand exactly the wtd thresholds configured in egress queue set
> command
>
> the following is an example from the documentation CD:
>
>
> Switch(config)# mls qos queue-set output 2 buffers 40 20 20 20
>
> Switch(config)# mls qos queue-set output 2 threshold 2 40 60 100 200
>
> let's take an example is we have 400 buffers, then the first command
> will allocate 40% for queue 1 and 20 percent for queue 2,3,4 --->
> queue 1 will be 160 buffer, queue 2-4 wil be 80 buffer
>
>
>
> for the second commad there is fine tuning in queue 2 i don't
> understand deeply the configured values for drop threshold 1 and drop
> threshold 2 ( 40 & 60) and I don't understand what they are
> configured for.
>
>
>
> the other two values I think they are as follow: 100 is the guaranteed
> memory for the queue, it means the queue will ot put any excess
> buffers to the allocated pools
>
> and value 200 means that the queue can borrow double the the allocated
> buffers---. ( 160x2) in case there is congetion, more than that it
> will drop packets and I have another question here does 200 percent
> means it will bowwo 160x2 buffers or will borrow only 160 additional
>
>
>
> Please appreciate if any one can help because the doc cd is nit clear
> at all, or if any body has a good documentation for that
>
> thanks
>
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