Strict-Priority Queue Overview

You can configure one queue per interface to have strict-priority, which causes delay-sensitive traffic, such as voice traffic, to be removed and forwarded with minimum delay. Packets that are queued in a strict-priority queue are removed before packets in other queues, including high-priority queues.

The strict-high-priority queuing feature allows you to configure traffic policing that prevents lower priority queues from being starved. The strict-priority queue does not cause starvation of other queues because the configured policer allows the queue to exceed the configured bandwidth only when other queues are not congested. If the interface is congested, the software directs strict-priority queues to the configured bandwidth.

To prevent queue starvation of other queues, you must configure an output (egress) policer that defines a limit for the amount of traffic that the queue can service. The software services all traffic in the strict-priority queue that is under the defined limit. When strict-priority traffic exceeds the limit, the policer marks the traffic in excess of the limit as out-of-profile. If the output port is congested, the software drops out-of-profile traffic.

You can also configure a second policer with an upper limit. When strict-priority traffic exceeds the upper limit, the software drops the traffic in excess of the upper limit, regardless of whether the output port is congested. This upper-limit policer is not a requirement for preventing starvation of the lower priority queues. The policer for the lower limit, which marks the packets as out-of-profile, is sufficient to prevent starvation of other queues.