> # About the DWRR Traffic Scheduler Queue

> The DWRR scheduler services the queues in the ratio of the configured weights. Higher weights translate to proportionally higher bandwidth and lower latency. The default weights are 50 for the high queue, 30 for the medium queue, and 20 for the low queue. The Cisco NX-OS software supports four scheduling queues:

> - Strict priority queues are queues that are serviced in preference to other queues—it is always serviced if there is a frame queued in it regardless of the state of the other queues.
> - QoS assigns all other traffic to the DWRR scheduling high, medium, and low priority traffic queues.

> The Cisco NX-OS software supports four scheduling queues:

> - Strict priority queues are queues that are serviced in preference to other queues—it is always serviced if there is a frame queued in it regardless of the state of the other queues.
> - QoS assigns all other traffic to the DWRR scheduling high, medium, and low priority traffic queues.

> The DWRR scheduler services the queues in the ratio of the configured weights. Higher weights translate to proportionally higher bandwidth and lower latency. The default weights are 50 for the high queue, 30 for the medium queue, and 20 for the low queue. Decreasing order of queue weights is mandated to ensure the higher priority queues have a higher service level, though the ratio of the configured weights can vary (for example, one can configure 70:30:5 or 60:50:10 but not 50:70:10).

> Table 11-2 describes the QoS behavior for Generation 1, Generation 2, and Generation 3 switching modules.

> Table 11-2 QoS Behavior for Generation 1 and Generation 2 Switching Modules
> Source Module Type | Destination Module Type | QoS Behavior Description
> --- | --- | ---
> Generation 1 | Generation 1 | QoS behavior reflects the DWRR configuration for traffic coming in through a given port and queued to the same egress port. All the other traffic share equal bandwidth.
> Generation 1 | Generation 2 or Generation 3 | QoS behavior reflects the DWRR configuration for traffic coming in through a given port and queued to the same egress port. All the other streams share equal bandwidth.
> Generation 2 or Generation 3 | Generation 1 | Bandwidth partitioning is equal for all the traffic.
> Generation 2 or Generation 3 | Generation 2 or Generation 3 | QoS behavior reflects the DWRR weights configuration for all possible streams.

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