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Cisco Bug: CSCvu55154 - On NCS55xx, WRED drop thresholds and queue-limit are not honored for PFC enabled queues

Last Modified

Sep 16, 2020

Products (1)

  • Cisco ASR 9000 Series Aggregation Services Routers

Known Affected Releases

7.3.1.BASE 7.4.1.BASE

Description (partial)

Release-note

Symptom:
On NCS55xx, WRED drop thresholds and queue-limit are not honored on PFC enabled queues
If ECN enabled is also enabled, ECN marking works fine with the same thresholds.

WRED works as usual on non-PFC enabled queues in the same NPU / system

Conditions:
On PFC enabled queues, the following configuration has no effect in class-map
unless it is used along with random-detect ecn

   random-detect <discard-class 0|1|2|3> [min threshold] [max threshold]

(discard-class is optional but the problem described is still valid even if discard-class is not used)

Similarly, queue-limit <> has no effect and traffic is buffered up to xoff+headroom for that traffic-class

On non-PFC enabled queues in the same system, these configuration work as usual
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