Queuing: Custom and Priority Queuing (CQ+PQ) + Queueing Strategies

29 May


Priority Queuing (PQ)

The “next level” of queuing is Priority Queuing (PQ), where four predefined queues exist: High, Medium, Normal, and Low. Traffic is placed into one of these four queues through the use of access lists and priority lists. The High queue is also called the strict priority queue, making PQ and LLQ the queueing solutions to use when a priority queue is needed.

These four queues are predefined, as are their limits:

  • High-Priority Queue: 20 Packets
  • Medium-Priority Queue: 40 Packets
  • Normal-Priority Queue: 60 Packets
  • Low-Priority Queue: 80 Packets

Important Concept for PQ:

PQ is not round-robin; when there are packets in the High queue, they’re going to be sent before any packets in the lower queues. (If too many traffic types are configured to go into the High and Medium queues, packets in the Normal and Low queues may never be sent)

R3(config)#priority-list 1 protocol ip ? high…

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