I've been trying to understand how QoS applied to sub-interfaces works, and cannot find any clear explanation.
My understanding is that a router configured with a number of sub-interfaces, no QoS applied, then each can have up to the physical line speed as its based on the clock rate of the attached circuit. If more than 1 subinterface is transmiting at once then the line speed bandwidth is shared between those active subinterfaces.
I was asked What happens if QoS is applied to only 1 of those subinterfaces, a parent policer and priority queue in a child policy on 1 subinterface?
My initial response was that a QoS policy should be applied to all subinterfaces, that seemed the correct way to do this, but, after reading through documentation I'm not sure that QoS on every subinterface is required..
Would the priority queue applied to one subinterface give traffic in that queue precedence over all the rest of the subinterfaces?
The example is where all subinterfaces are data only, apart from 1 which has a mix of voice and data.