priority command policing confusion

[carl_townshend]

Hi all

I have some confusion with the priority command, I read a Cisco doc that says the priority queue is allowed to use above its configured rate? is this true? as what happens if additional traffic comes in?

we use the command priority percent 33 for example, would this police it to 33% and not allow it to use more? or does it allow you to use more? or would you need to use the below to police

>class-map xx

priority

police xxxx

I am confused?

The doc in question is here,

https://www.cisco.com/c/en/us/support/docs/quality-of-service-qos/qos-packet-marking/10100-priorityvsbw.html

[Joseph W. Doherty]

Typically, the way the CBWFQ priority command works, it provides an implicit policer that only engages if there's congestion.

If you need to guarantee that a priority class will never exceed its bandwidth allocation, you need to use an explicit policer (or shaper).

[carl_townshend]

so what would happen if I type  police percent 33

does that mean it can use the whole link? what if its not congested but other traffic on the link?

[Joseph W. Doherty]

If the interface is not congested, your priority class could use all 100% (or whatever is not used by other traffic - for latter, aggregate cannot exceed 100%).

Once the interface becomes congested, the policed value is enforced.