Need help setting up QoS on a 3850 at a remote site

[spfister336]

I have a 3850 which serves as the core switch at a remote site. The gig interface leading to the upstream provider (set to 100mbps, which is the upstream bandwidth) is showing several bursts of discards during the day, as well as an equal number of transmit errors (which seem to match a known bug). We've had complaints of slow file transfers to our central office.

Port        Align-Err     FCS-Err    Xmit-Err     Rcv-Err  UnderSize  OutDiscards
Gi1/0/23            0           0     7412585           0          0      7412585

This switch was not set up with a service-policy for QoS, and I'm assuming this is something I'm going to need to do. I'm a little rusty at QoS, and I'd like some help in getting it set up. We have QoS set up at

many other sites (non-3850s) for comparison.

[Joseph W. Doherty]

I haven't worked with any 3650/3850, and although I believe their QoS is improved over the prior 3650/3750 series, their default buffering may still require tuning to minimize drops. See if your 3850's QoS chapter has any mention on adjusting QoS buffering.

On the prior 3650/3750, when you enabled QoS, some buffer space was tied to each interface's QoS queues, even if all traffic was only using one queue or few interfaces. I found reducing the interface queue reservations, and allowing interfaces to grab additional buffers, often dramatically reduced drops due to insufficient buffers. Again, this may not pertain to the 3850, but you might check.