[c-nsp] WRR Confusion on 6748 blades

[Janez Novak]

6748 can't do shaping. Would love to have them do that. So you must be
experiencing drops somewhere else and not from WRR BW settings or WRED
settings. They both kick in when congestion is happening (queues are
filling up). For exaple linecard is oversubscribed etc

Look at second bullet
(http://www.cisco.com/en/US/docs/routers/7600/ios/12.2SR/configuration/guide/qos.html#wp1728810).

Kind regards,
Bostjan

On Tue, Jun 26, 2012 at 10:28 PM, Chris Evans <chrisccnpspam2 at gmail.com> wrote:
> Tac is right. This is a downfall of ethernet switching qos. The buffers are
> carved up for the queues. My advice is to disable qos altogether or remap
> all traffic and buffers  back to one queue.
> On Jun 26, 2012 4:22 PM, "John Neiberger" <jneiberger at gmail.com> wrote:
>
>> I'm getting conflicting information about how WRR scheduling and
>> queueing works on 6748 blades. These blades have three regular queues
>> and one priority queue. We've been told by two Cisco TAC engineers
>> that if one queue is full, packets will start being dropped even if
>> you have plenty of link bandwidth available. Our experience over the
>> past few days dealing with related issues seems to bear this out. If a
>> queue doesn't have enough bandwidth allotted to it, bad things happen
>> even when the link has plenty of room left over.
>>
>> However, someone else is telling me that traffic should be able to
>> burst up to the link speed as long as the other queues are not full.
>> Our experience seems to support what we were told by Cisco, but we may
>> just be looking at this the wrong way. It's possible that the queue
>> only seems to be policed, but maybe most of the drops are from RED.
>> I'm just not sure now.
>>
>> Can anyone help clear this up?
>>
>> Thanks!
>> John
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