From: Anwar Chalamannil (anwar.chalamannil@gmail.com)
Date: Wed Dec 07 2005 - 02:59:37 GMT-3
Hi Paresh ,Chris and all
According to the docCD
Traffic shaping and policing are not currently supported with CBWFQ. (
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos_c/fqcprt2/qcfconmg.htm
If you want to use CBWFQ with the Class-Based Traffic Shaping mechanism, the
following conditions must be met:
A secondary-level (child) policy map *must* be created. This
secondary-level (child) policy map is then used to configure CBWFQ by
enabling the *bandwidth* command.
Traffic shaping *must* be configured in the primary-level (parent) policy
map.
But As Paresh showed the configuration commands are well accepted on the
router .
Any explanations ??
Thanks
Anwar
On 12/5/05, Paresh Khatri <Paresh.Khatri@aapt.com.au> wrote:
>
> Thanks Chris.. I suspected I would not get a definitive answer to this but
> it
> was worth a shot :-)
>
> Cheers,
> Paresh.
>
> -----Original Message-----
> From: Chris Lewis [mailto:chrlewiscsco@yahoo.com]
> Sent: Monday, 05 December 2005 01:06 PM
> To: Paresh Khatri; Cisco certification
> Subject: Re: MQC: Using 'shape' with 'bandwidth'
>
>
> Paresh,
>
> It looks like you have a good undersatnding of what you need for the lab
> exam
> on this topic, going beyond that gets a bit tricky and there is not
> exactly
> one answer, it can change depending on hardware.
>
> The way I discuss this with customers is at a level that considers the
> followiong:
>
> For egress, packets get placed in to a class, the per class policy is
> applied,
> then packets enter the frame relay shaper. After the shaper there is
> either a
> single FIFO or a dual FIFO depending on FRF.12 configuration. If single
> FIFO,
> all packets go in to that, if dual FIFO, voip packets can bypass the frame
> shaper depending on platform capabilities.
>
> Chris
>
> Paresh Khatri <Paresh.Khatri@aapt.com.au> wrote:
>
> 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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