Configuring Congestion Management (Interface Mode)

Pre-configuration Tasks

Before configuring congestion management, map the priority of packets to a PHB.

Context

Configure congestion management on the device when the network intermittently becomes congested.

Once congestion management is configured, the sequence at which packets are forwarded is determined according to the defined scheduling policy. High-priority services are scheduled preferentially.

There are eight queues on each interface. Different queues can use different scheduling modes, but each queue can use only one scheduling mode. Scheduling modes supported on the device include PQ, WRR, WDRR, PQ+WRR, and PQ+WDRR. When PQ+WRR or PQ+WDRR scheduling mode is used, the device schedules the queues using PQ scheduling first. If multiple queues using PQ scheduling exist, the device schedules the queues in descending order of priority. A larger queue index indicates a higher priority. After PQ scheduling is completed, the device schedules the queues using WRR or WDRR scheduling.

Both WRR and WDRR use weights. WRR schedules packets in queues based on the number of packets, whereas WDRR schedules packets in queues based on the number of bytes.

For GE interfaces (including XGE interfaces configured with GE optical modules) on the S5731-H, S5731-S, S5731S-H, and S5731S-S, if severe congestions occur, queue scheduling is inaccurate on these interfaces, and traffic forwarding may even be interrupted in some low-priority queues. To prevent this, you are advised to configure congestion avoidance.

Only the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S5735-L, S5735S-L, S5735S-L-M, S5735-S, S5735S-S, S5735-S-I, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S support congestion management in interface mode.

Procedure

Run system-view
The system view is displayed.
Run interface interface-type interface-number
The interface view is displayed.
Run qos { pq | wrr | drr }
The scheduling mode of queues on the interface is set to PQ, WRR, or WDRR.

By default, the scheduling mode of queues on an interface of the S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-HI, S6730-H, S6730S-H, S6730-S, and S6730S-S is WDRR, and the scheduling mode of queues on an interface of other models is WRR.
Configure the weight.
- In WRR scheduling, run qos queue queue-index wrr weight weight
  
  The weight for WRR scheduling is set.
  
  By default, the weight for WRR scheduling is 1.
  
  This step is required only when the scheduling mode is WRR or PQ+WRR.
  
  When WRR scheduling is applied and the weight of a queue is set to 0, PQ scheduling is used. That is, the queue uses PQ+WRR.
  
  The S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-HI, S6730-H, S6730S-H, S6730-S, and S6730S-S do not support WRR or PQ+WRR.
- In WDRR scheduling, run qos queue queue-index drr weight weight
  
  The weight for WDRR scheduling is set.
  
  By default, the weight for WDRR scheduling is 1.
  
  This step is required only when the scheduling mode is WDRR or PQ+WDRR.
  
  When WDRR scheduling is applied and the weight of a queue is set to 0, PQ scheduling is used. That is, the queue uses PQ+WDRR.
  
  On the S5720-EI, if the queue scheduling mode is changed or the weight is changed during queue scheduling, packet loss occurs within 250 ms.
  
  On the S6720-EI and S6720S-EI, if the queue scheduling mode is changed or the weight is changed during queue scheduling, packet loss occurs within 20 ms.

Verifying the Configuration

Run the display qos configuration interface [ interface-type interface-number ] command to check all the QoS configurations on the interface.
Run the display qos queue statistics interface interface-type interface-number [ queue queue-index ] command to view queue-based traffic statistics on the interface.