NOTE: Although, each port on the S4810, S4820T, and S5000 devices support 8 QoS queues, you can configure only 4QoS queues (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 fromthe interface.Lossless traffic egresses out the no-drop queues. Ingress dot1p traffic from PFC-enabled interfaces is automatically mapped to theno-drop egress queues.1. Enter INTERFACE Configuration mode.CONFIGURATION modeinterface type slot/port[/subport]2. 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 range is from 0 to 3. Separate the 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.The default: No lossless queues are configured.NOTE: Dell Networking OS Behavior: By default, no lossless queues are configured on a port.A limit of two lossless queues is supported on a port. If the amount of priority traffic that you configure to be paused exceeds thetwo lossless queues, an error message displays.Configuring PFC in a DCB MapAn S4048–ON switch supports the use of a DCB map in which you configure priority-based flow control (PFC) setting. To configurePFC parameters, you must apply a DCB map on an S4048–ON interface. This functionality is supported on the S4048–ON platform.PFC Configuration NotesPFC provides flow control based on the 802.1p priorities in a converged Ethernet traffic that is received on an interface and isenabled by default when you enable DCB. As an enhancement to the existing Ethernet pause functionality, PFC stops traffictransmission for specified priorities (CoS values) without impacting other priority classes. Different traffic types are assigned todifferent priority classes.When traffic congestion occurs, PFC sends a pause frame to a peer device with the CoS priority values of the traffic that needs tobe stopped. DCBx provides the link-level exchange of PFC parameters between peer devices. PFC allows network administrators tocreate zero-loss links for SAN traffic that requires no-drop service, while at the same time retaining packet-drop congestionmanagement for LAN traffic.On switch, PFC is enabled by default on Ethernet ports (pfc mode on command). You can configure PFC parameters using aDCB map or the pfc priority command in Interface configuration mode. For more information, see Configuring Priority-BasedFlow Control.248 Data Center Bridging (DCB)
