QoS problems often come from configuration mistakes. Knowing common issues helps troubleshooting.
Marking not preserved:
- DSCP changes between hops
- Cause: Trust boundary misconfigured
- Fix: Verify trust at each boundary
Voice quality poor despite QoS:
- Latency or jitter still high
- Cause: Congestion upstream of QoS device
- Fix: Enable QoS end-to-end
Traffic not getting bandwidth:
- Classification not matching
- Cause: Wrong match criteria
- Fix: Test with packet captures
Everything in default class:
- All traffic falls to best effort
- Cause: Class maps too specific
- Fix: Review classification rules