command is used to specify that a class of traffic has latency requirements
with respect to other classes. For multiple priority queues, you can use the
command to configure a level of priority service on a class in a policy map.
Currently, the device supports two priority levels: level 1 (high) and level 2
(low). The device places traffic with a high-priority level on the outbound
link ahead of traffic with a low-priority level. High-priority packets,
therefore, are not delayed behind low-priority packets.
The device services
the high-level priority queues until empty before servicing the next-level
priority queues and non-priority queues. While the device services a queue, the
service rate is as fast as possible and is constrained only by the rate of the
underlying link or parent node in a hierarchy. If a rate is configured and the
device determines that a traffic stream has exceeded the configured rate, the
device drops the exceeding packets during periods of congestion. If the link is
currently not congested, the device places the exceeding packets onto the
When configuring MPQ
on different traffic classes in a policy map, you must specify different
priority levels for the traffic classes. For example, configure one traffic
class to have priority level 2 and another class to have priority level 1.
In a hierarchical MPQ configuration in which all traffic is sent through the level-2 priority queue
only, the traffic sent through the level-2 priority queue receives the same
treatment as the traffic sent through the level-1 priority queue.
traffic is not policed appropriately, bandwidth starvation of low-priority
traffic can occur. Therefore, though not required, we recommend that you
configure a policer for high-priority traffic using the
If you configure the
for priority queues, the traffic rate is policed to the police rate for each of
the priority queues.
You cannot configure
command and the
command on different classes in the same policy map.