[c-nsp] WRR Confusion on 6748 blades

[John Neiberger]

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