[QoS] When to enable fair-queue in class-default?

[jackawang]

When the requirement does not explicitly mention "fair queue", should we enable fair-queue in class-default? I understand it is probably better practice by having fair-queue enabled but I'd like to know the cons and side effects it may have.

Say I have a class-baded LLQ configured for voice.

policy-map VOIP-POLICY

class VOIP-CLASS

  priority 20

class DATA-CLASS

  bandwidth 40

class class-default

  fair-queue   <--- is it necessary?

!

[jackawang]

Nobody knows?

[ajay chauhan]

WFQ is the default queueing mode on interfaces that run at or below E1 speeds (2.048 Mbps or less). You can Also Configure threshold .

For DWFQ, packets are classified by flow. Packets with the same source IP address, destination IP address, source TCP or UDP port, destination TCP or UDP port, and protocol belong to the same flow.

Defaults are provided for the congestion threshold after which messages for high-bandwidth conversations are dropped, and for the number of dynamic and reservable queues; however, you can fine-tune your network operation by changing these defaults.

ty