From: Arun Arumuganainar (aarumuga@hotmail.com)
Date: Mon Dec 05 2005 - 07:58:44 GMT-3
The behavior is as follow .
When there is no congestion : Traffic will be shaped to 256 KBPS .
When there is congestion : Shaping will be still done . But Bandwidth
allocated to shaped traffic will be limited to 128KBPS .
Hope this helps .
Thanks and Regards
Arun
----- Original Message -----
From: "Paresh Khatri" <Paresh.Khatri@aapt.com.au>
To: "Cisco certification" <ccielab@groupstudy.com>
Sent: Monday, December 05, 2005 6:00 AM
Subject: MQC: Using 'shape' with 'bandwidth'
> Hi all,
>
> I'm trying to get an understanding of how the 'shape' command works when
used together with a 'bandwidth' command.
>
> For example:
>
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> class-map match-all prec3
> match ip precedence 3
> !
> policy-map PolOut4
> class prec3
> bandwidth 128
> shape average 256000
>
> router#sh policy-map PolOut4
> Policy Map PolOut4
> Class prec3
> Bandwidth 128 (kbps) Max Threshold 64 (packets)
> Traffic Shaping
> Average Rate Traffic Shaping
> CIR 256000 (bps) Max. Buffers Limit 1000 (Packets)
> router#
>
> router#sh policy-map int fast0/0 output
> FastEthernet0/0
>
> Service-policy output: PolOut4
>
> Class-map: prec3 (match-all)
> 0 packets, 0 bytes
> 5 minute offered rate 0 bps, drop rate 0 bps
> Match: ip precedence 3
> Queueing
> Output Queue: Conversation 265
> Bandwidth 128 (kbps) Max Threshold 64 (packets)
> (pkts matched/bytes matched) 0/0
> (depth/total drops/no-buffer drops) 0/0/0
> Traffic Shaping
> Target/Average Byte Sustain Excess Interval Increment
> Rate Limit bits/int bits/int (ms) (bytes)
> 256000/256000 1984 7936 7936 31 992
>
> Adapt Queue Packets Bytes Packets Bytes Shaping
> Active Depth Delayed Delayed Active
> - 0 0 0 0 0 no
>
> Class-map: class-default (match-any)
> 41 packets, 5096 bytes
> 5 minute offered rate 0 bps, drop rate 0 bps
> Match: any
> router#
>
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> I don't have any problems with the intent of such a configuration. The
bandwidth will determine the minimum rate at which the prec3 queue will be
serviced under congestion whereas the shaping rate will be the maximum rate
at which the queue will be serviced. Based on my testing, all of this works
quite well.
>
> My confusion is with the order of operations and the queue sizes. The
output of 'show policy-map' indicates a max buffers of 1000 (for the shaping
queue) and a threshold of 64 packets for the CBWFQ queue. However, the
output of 'show policy-map' interface does not show the max buffers for
shaping. Are there two separate queues used when using such a configuration
? If so, what is the order of operations here ?
>
> Here is what I consider to be the three options:
> 1. There are 2 queues where the shaping queue follows the CBWFQ queue.
> The output of the CBWFQ queue enters the shaping queue from which packets
are leaked out based on the shaping parameters. This would satisfy the
shaping requirement of the class. At each scheduling interval, the router
would schedule packets out of the CBWFQ and into the shaping queue. At the
same time it would de-queue packets from the head of the shaping queue at a
rate that does not exceed the shaping rate. Therefore, for classes for
which shaping is configured, packets destined for the TxQ would only be
de-queued from the shaping queue (because packets de-queued from the CBWFQ
queue would enter the shaping queue). For classes for which shaping is not
configured, packets are dequeued directly from the CBWFQ queue and into the
TxQ.
>
> 2. There are 2 queues where the CBWFQ queue follows the shaping queue.
> The output of the shaping queue enters the CBWFQ queue from which packets
are leaked out based on the shaping parameters. The router would give the
CBWFQ queue sufficient credits in each shceduling interval so that the
shaping rate is not exceeded. In this case, the shaping queue is there
purely to provide additional buffer space. The scheduling of packets is
consistent for all classes in this case (whether or not they use shaping) -
all packets are de-queueud from the CBWFQ and send to the TxQ.
>
> 3. There is just one queue which is used for CBWFQ and shaping.
> In this case, it would make sense that the queue is the size of the
shaping queue (1000 packets, by default). The router would give the CBWFQ
queue sufficient credits in each scheduling interval so that the shaping
rate is not exceeded.
>
> Alright, so that's what I am grappling with at the moment. So which of
the above is it ? Or am I totally off the mark and there is some other way
this is done.
>
> All comments appreciated.
> Paresh.
>
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