120 | Data Center Bridging (DCB)w w w . d e l l . c o m | s u p p o r t . d e l l . c o mConfiguring Priority-Based Flow ControlPriority-based flow control provides a flow control mechanism based on the 802.1p priorities in convergedEthernet traffic received on an interface and is enabled by default. As an enhancement to the existingEthernet pause mechanism, PFC stops traffic transmission for specified priorities (CoS values) withoutimpacting other priority classes. Different traffic types are assigned to different priority classes.When traffic congestion occurs, PFC sends a pause frame to a peer device with the CoS priority values ofthe traffic that needs to be stopped. DCBX provides the link-level exchange of PFC parameters betweenpeer devices. PFC allows network administrators to create zero-loss links for SAN traffic that requiresno-drop service, while at the same time retaining packet-drop congestion management for LAN traffic.To ensure complete no-drop service, you must apply the same DCB input policy with the same pause timeand dot1p priorities on all PFC-enabled peer interfaces.To configure PFC and apply a PFC input policy to an interface, follow these steps:Step Task Command Command Mode1 Create a DCB input policy to apply pause or flowcontrol for specified priorities using a configured delaytime.Maximum: 32 alphanumeric characters.dcb-input policy-name CONFIGURATION2 Configure the link delay used to pause specified prioritytraffic.One quantum is equal to a 512-bit transmission.Valid values (in quanta): 712-65535.Default: 45556 quantum in link delay.pfc link-delay value DCB INPUT POLICY3 Configure the CoS traffic to be stopped for the specifieddelay. Enter the 802.1p values of the frames to bepaused.Valid values: 0-7.Default: None.Maximum number of loss less queues supported on theswitch: 2.Separate priority values with a comma; specify apriority range with a dash; for example: pfc priority1,3,5-7.pfc priority priority-range DCB INPUT POLICY4 Enable the PFC configuration on the port so that thepriorities are included in DCBX negotiation with peerPFC devices. Default: PFC mode is on.pfc mode on DCB INPUT POLICY5 (Optional) Enter a text description of the input policy.Maximum: 32 characters.description text DCB INPUT POLICY6 Exit DCB input policy configuration mode. exit DCB INPUT POLICY7 Enter interface configuration mode. interface type slot/port CONFIGURATION8 Apply the input policy with the PFC configuration to aningress interface.dcb-policy inputpolicy-nameINTERFACE9 Repeat Steps 1 to 8 on all PFC-enabled peer interfaces to ensure lossless traffic service.
