The pfc on command enables priority-based flow control.3 Specify the dot1p priority-to-priority group mapping for each priority.priority-pgid dot1p0_group_num dot1p1_group_num ...dot1p7_group_numPriority group range is from 0 to 7. All priorities that map to the same queue must be in the same priority group.Leave a space between each priority group number. For example: priority-pgid 0 0 0 1 2 4 4 4 in which priority group 0 maps to dot1ppriorities 0, 1, and 2; priority group 1 maps to dot1p priority 3; priority group 2 maps to dot1p priority 4; priority group 4 maps to dot1ppriorities 5, 6, and 7.Dell Networking OS Behavior: As soon as you apply a DCB policy with PFC enabled on an interface, DCBx starts exchanging informationwith PFC-enabled peers. The IEEE802.1Qbb, CEE, and CIN versions of PFC Type, Length, Value (TLV) are supported. DCBx also validatesPFC configurations that are received in TLVs from peer devices.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 1, 2 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:NOTE: Although, each port on the S4810, S4820T, and S5000 devices support 8 QoS queues, you can configure only 4 QoSqueues (0-3) to manage data traffic. The remaining 4 queues (4-7) are reserved for control traffic.Dell(conf)#do show qos dot1p-queue-mappingDot1p Priority : 0 1 2 3 4 5 6 7Queue : 0 0 0 1 2 3 3 3Dell(conf)#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 modeData Center Bridging (DCB) 259
