[c-nsp] WRR Confusion on 6748 blades

[John Neiberger]

On Wed, Jun 27, 2012 at 9:58 AM, John Neiberger <jneiberger at gmail.com> wrote:
> On Wed, Jun 27, 2012 at 8:24 AM, Janez Novak <jnovak123 at gmail.com> wrote:
>> 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
>
> This is very confusing and I'm getting a lot of conflicting
> information. I've been told by three Cisco engineers that these queue
> bandwidths limits are fairly hard limits. That is in line with what we
> were experiencing because we were seeing output queue drops when the
> interface was not fully utilized. Increasing the queue bandwidth got
> rid of the output queue drops. For one particular application
> traversing this link, that resulted in a file transfer rate increase
> from 2.5 MB/s to 25 MB/s. That's a really huge difference and all we
> did was increase the allocated queue bandwidth. At no point was that
> link overutilized. In fact, during our testing of that particular
> application, the link output never went above 350 Mbps. We used very
> large files so that the transfer would take a while and we'd get a
> good feel for what was happening. Doing nothing but increasing the
> queue bandwidth fixed the problem there and has fixed the same sort of
> issue elsewhere.
>
> I'm still researching this and trying to get to the bottom of it. I
> think we're missing something important that would make this all make
> more sense. I appreciate everyone's help!
>
> John

Also, these 6748 linecards are 1p3q8t. According to that doc these use
DWRR. Does the second bullet apply to DWRR, as well? I'm not quite
sure of the differences.

Thanks again,
John