C9300 - Priority queue not taking unused bandwidth

[Nadav]

Hi everyone,

I'm testing the cat9300 series on 16.12.x software.

Here is the policy-map used on the outgoing wired interface (service-policy output):

=========================

policy-map myPolicyMap
class ClassA
priority level 1 1000
class ClassB
bandwidth 500
class ClassC
bandwidth 4300
random-detect dscp-based
class class-default
bandwidth 200
random-detect dscp-based

policy-map parentPolicyMap
class class-default
shape average 6000000
service-policy myPolicyMap

=========================

The egress interface uses no more than 1000kbps for ClassA traffic, even though it has 5Mbps to spare. I've changed the priority level bandwidth to 1500, and the egress interface then uses no more than 1500kbps for that class.

Priority queue traffic can't use bandwidth that isn't in use by other classes in the policy.

This is different than ISR 4k and ASR 1k behavior, which both have been tested in the past and priority queue takes spare bandwidth for those devices. 

Any chance this is the expected behavior for Cat 9k? Is it documented? 

Thanks!

[Georg Pauwen]

Hello,

try and remove the default class from the child policy:

policy-map myPolicyMap
class ClassA
priority level 1 1000
class ClassB
bandwidth 500
class ClassC
bandwidth 4300
random-detect dscp-based
--> no class class-default
bandwidth 200
random-detect dscp-based

!

policy-map parentPolicyMap
class class-default
shape average 6000000
service-policy myPolicyMap

[Nadav]

Hi,

Tried removing class-default, but am seeing the same symptoms.

Besides, I'd like to have WRED and a set bandwidth for the default class.

[Joseph W. Doherty]

Cannot say how the 9300L's PQ should behave (traditionally switch PQ takes all the bandwidth it wants) but on an ISR or ASR LLQ has an implicit policer. It's true, with the latter, that the policer doesn't appear to engage when there's "spare" bandwidth, but perhaps that's not true on a 9300L.

[Nadav]

Using a regular 9300, not the 9300L. 

Hopefully someone can give us some insight regarding the expected behavior for this platform and whether it can be circumvented.