We have this config on a few switches operating as L3 switches in spoke LANs, linking back to a central location. Backups run from the spokes to the main office over these switches at night, and the data transfer rates are inexplicably slow. Looking at the WAN links out from the switches, I can see that there is only about 5% utilization over the night period, and the backup software is not throttling.
Would this QoS setup throttle traffic on a link that is otherwise not being utilized? As I understand, that's not how it should work at all, higher priority queues should be served first, but if there's no traffic in them, the lower priority ones should be fine. I'm open to suggestions however!
Capture the output of "show platform port-asic stat drop" multiple times and see if you see TxQueue drop counters incrementing for any port. If you do, traffic would be getting dropped because of QoS configuration.
If you know the interfaces on this switch which could be dropping packets, perform "show platform pm if-num" and find out the internal port associated with that physical interface. Once you know the internal port, "sh platform port-asic stat drop port " will tell you if traffic is being dropped in its queues.
Hope this helps.
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