NOTE: You cannot enable PFC and link-level flow control at the same time on aninterface.Configuring Lossless QueuesDCB also supports the manual configuration of lossless queues on an interface when PFC mode is turned off.Prerequisite: A DCB with PFC configuration is applied to the interface with the following conditions:• PFC mode is off (no pfc mode on).• No PFC priority classes are configured (no pfc priority priority-range).Example:Port A —> Port BPort C —> Port BPFC no-drop queues are configured for queues 3, 4 on Port B. PFC capability is enabled on priorities 3, 4 on PORT A and C.Port B acting as EgressDuring the congestion, [traffic pump on priorities 3 and 4 from PORT A and PORT C is at full line rate], PORT A and C send out the PFCsto rate the traffic limit. Egress drops are not observed on Port B since traffic flow on priorities is mapped to loss less queues.Port B acting as IngressIf 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:The configuration of no-drop queues provides flexibility for ports on which PFC is not needed but lossless traffic should egress from theinterface.Lossless traffic egresses out the no-drop queues. Ingress dot1p traffic from PFC-enabled interfaces is automatically mapped to the no-dropegress queues.1 Enter INTERFACE Configuration mode.CONFIGURATION modeinterface type slot/port2 Configure the port queues that will still function as no-drop queues for lossless traffic.INTERFACE modepfc no-drop queues queue-rangeFor the dot1p-queue assignments, refer to the dot1p Priority-Queue Assignment table.The maximum number of lossless queues globally supported on the switch is two.The default: No lossless queues are configured.3 Configure to drop the unknown unicast packets flooding on lossless priorities.CONFIGURATION modepfc-nodrop-priority l2-dlf drop4 View the packets drop count corresponding to the priority.EXEC modeEXEC Privilege modeData Center Bridging (DCB) 253
