priority [kbps|percent n]
Configures strict priority queuing for a class in a policy map, optionally specifying bandwidth in kbps or as a percentage of the interface bandwidth.
priority [kbps|percent n]When to Use This Command
- Guarantee low latency for real-time traffic like VoIP by assigning strict priority to the voice class.
- Ensure critical control plane traffic (e.g., routing protocols) is prioritized over bulk data.
- Provide priority for video conferencing traffic to avoid jitter and packet loss.
- Allocate a percentage of bandwidth to a priority queue for interactive applications.
Command Examples
Basic priority with bandwidth in kbps
priority 128Router(config-pmap-c)# priority 128 Router(config-pmap-c)#
No output is generated; the command is accepted silently. The class will receive strict priority up to 128 kbps.
Priority with percentage
priority percent 30Router(config-pmap-c)# priority percent 30 Router(config-pmap-c)#
No output; the class will receive strict priority up to 30% of the interface bandwidth.
Understanding the Output
The priority command does not produce any output when entered. To verify the configuration, use 'show policy-map [policy-map-name]' or 'show policy-map interface [interface]'. In the output, look for the class with priority configured. The 'Strict Priority' or 'Priority' field indicates the bandwidth allocated (e.g., 128 kbps or 30%). If the priority queue is congested, packets exceeding the bandwidth limit are dropped. A healthy configuration shows no excessive drops in the priority queue.
CCNA Exam Tips
Remember that priority queuing can cause starvation of other queues if not policed; CCNA expects you to know that priority should be used sparingly.
The 'priority' command is only available in policy-map class configuration mode; it cannot be used in the default class.
When using 'priority percent', the percentage is based on the interface bandwidth, not the remaining bandwidth.
Be aware that priority and bandwidth commands are mutually exclusive within the same class; you cannot use both.
Common Mistakes
Mistake 1: Using 'priority' without specifying a bandwidth limit, which defaults to unlimited and can starve other traffic.
Mistake 2: Applying priority to the default class (class-default) — this is not allowed and will be rejected.
Mistake 3: Confusing 'priority' with 'bandwidth' — priority provides strict priority queuing, while bandwidth guarantees a minimum share.
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