Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.14.1.0 - Page 267
Priority-Based Flow Control Using Dynamic Buffer Method
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If the traffic congestion is on PORT B , Egress DROP is on PORT A or C, as the PFC is not enabled on PORT B. Refer the following configuration for queue to dot1p mapping: DellEMC(conf)#do show qos dot1p-queue-mapping Dot1p Priority : 0 1 2 3 4 5 6 7 -> On ingress interfaces[Port A and C] we used the PFC on priority level. Queue : 0 0 0 1 2 3 3 3 -> On Egress interface[Port B] we used no-drop queues. Lossless traffic egresses out the no-drop queues. Ingress 802.1p traffic from PFC-enabled peers is automatically mapped to the no-drop egress queues. When configuring lossless queues on a port interface, consider the following points: • By default, no lossless queues are configured on a port. • A limit of two lossless queues is supported on a port. If the number of lossless queues configured exceeds the maximum supported limit per port (two), an error message is displayed. Reconfigure the value to a smaller number of queues. • If you configure lossless queues on an interface that already has a DCB map with PFC enabled (pfc on), an error message is displayed. Table 17. Configuring Lossless Queues on a Port Interface Step Task 1 Enter INTERFACE Configuration mode. Command interface interface-type 2 Open a DCB map and enter DCB map configuration mode. dcb-map name 3 Disable PFC. no pfc mode on 4 Return to interface configuration mode. exit 5 Apply the DCB map, created to disable the PFC operation, dcb-map {name | default} on the interface 6 Configure the port queues that still function as no-drop pfc no-drop queues for lossless traffic. For the dot1p-queue assignments. queuesqueue-range The maximum number of lossless queues globally supported on a port is 2. You cannot configure PFC no-drop queues on an interface on which a DCB map with PFC enabled has been applied, or which is already configured for PFC using the pfc priority command. Range: 0-3. Separate queue values with a comma; specify a priority range with a dash; for example: pfc no-drop queues 1,3 or pfc no-drop queues 2-3 Default: No lossless queues are configured. Command Mode CONFIGURATION INTERFACE DCB MAP DCB MAP INTERFACE INTERFACE Priority-Based Flow Control Using Dynamic Buffer Method In a data center network, priority-based flow control (PFC) manages large bursts of one traffic type in multiprotocol links so that it does not affect other traffic types and no frames are lost due to congestion. When PFC detects congestion on a queue for a specified priority, it sends a pause frame for the 802.1p priority traffic to the transmitting device. Data Center Bridging (DCB) 267
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