Dell PowerSwitch S4820T 9.50.1 Configuration Guide for the S4820T System - Page 271
Configuring Priority-Based Flow Control, DCB INPUT POLICY mode
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Configuring Priority-Based Flow Control PFC provides a flow control mechanism based on the 802.1p priorities in converged Ethernet traffic received on an interface and is enabled by default when you enable DCB. As an enhancement to the existing Ethernet pause mechanism, PFC stops traffic transmission for specified priorities (Class of Service (CoS) values) without impacting 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 of the traffic that is to be stopped. Data Center Bridging Exchange protocol (DCBx) provides the link-level exchange of PFC parameters between peer devices. PFC allows network administrators to create zeroloss links for Storage Area Network (SAN) traffic that requires no-drop service, while retaining packetdrop congestion management for Local Area Network (LAN) traffic. To ensure complete no-drop service, apply the same DCB input policy with the same pause time and dot1p priorities on all PFC-enabled peer interfaces. To configure PFC and apply a PFC input policy to an interface, follow these steps. 1. Create a DCB input policy to apply pause or flow control for specified priorities using a configured delay time. CONFIGURATION mode dcb-input policy-name The maximum is 32 alphanumeric characters. 2. Configure the link delay used to pause specified priority traffic. DCB INPUT POLICY mode pfc link-delay value One quantum is equal to a 512-bit transmission. The range (in quanta) is from 712 to 65535. The default is 45556 quantum in link delay. 3. Configure the CoS traffic to be stopped for the specified delay. DCB INPUT POLICY mode pfc priority priority-range Enter the 802.1p values of the frames to be paused. The range is from 0 to 7. The default is none. Maximum number of loss less queues supported on the switch: 2. Separate priority values with a comma. Specify a priority range with a dash, for example: pfc priority 1,3,5-7. Data Center Bridging (DCB) 271
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