[c-nsp] WRR Confusion on 6748 blades

John Neiberger jneiberger at gmail.com
Wed Jun 27 11:58:48 EDT 2012


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


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