A few things we tend to forget when setting up QoS on routers:
- it is a good idea to decrease the tx-ring buffer (hardware queue) to the minimum size so that we have more control over the traffic in the software queue
- IOS considers congestion to be occurring when the hardware queue is full
- This means that we might have e.g. a 100mbit link, but with tx-ring decreased even small load will cause the router to believe there is congestion on the link. This means that our QoS output policy will kick in (good!)
- It is a good idea to always assign bandwidth to the class-default, otherwise unused bandwidth will be split across all configured classes.
- It is a bad idea to have one priority queue for voip + video traffic