Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.112.1P1 - Page 262

Strict-priority groups: If two priority groups have strict-priority scheduling, traffic assigned from the priority group with the higher priority-queue number is scheduled first. However, when three priority groups are used and two groups have strictpriority scheduling (such as groups 1 and 3 in the example), the strict priority group whose traffic is mapped to one queue takes precedence over the strict priority group whose traffic is mapped to two queues. Therefore, in this example, scheduling traffic to priority group 1 (mapped to one strict-priority queue) takes precedence over scheduling traffic to priority group 3 (mapped to two strict-priority queues). Using ETS to Manage Converged Ethernet Traffic To use ETS for managing converged Ethernet traffic, use the following command: dcb-map stack-unit all dcb-map-name Applying DCB Policies in a Switch Stack You can apply DCB policies with PFC and ETS configurations to all stacked ports in a switch stack or on a stacked switch. To apply DCB policies in a switch stack, follow this step. NOTE: Use only 40G ports as stacking ports when you enable DCB. S4820T does not support DCB when you use 10GBaseT ports as stacking ports. • Apply the specified DCB policy on all ports of the switch stack or a single stacked switch. CONFIGURATION mode dcb-map {stack-unit all | stack-ports all} dcb-map-name Configure a DCBx Operation DCB devices use data center bridging exchange protocol (DCBx) to exchange configuration information with directly connected peers using the link layer discovery protocol (LLDP) protocol. DCBx can detect the misconfiguration of a peer DCB device, and optionally, configure peer DCB devices with DCB feature settings to ensure consistent operation in a data center network. DCBx is a prerequisite for using DCB features, such as priority-based flow control (PFC) and enhanced traffic selection (ETS), to exchange link-level configurations in a converged Ethernet environment. DCBx is also deployed in topologies that support lossless operation for FCoE or iSCSI traffic. In these scenarios, all network devices are DCBx-enabled (DCBx is enabled end-to-end). For more information about how these features are implemented and used, refer to: • Configure Enhanced Transmission Selection DCBx supports the following versions: CIN, CEE, and IEEE2.5. Prerequisite: For DCBx, enable LLDP on all DCB devices. DCBx Operation DCBx performs the following operations: • Discovers DCB configuration (such as PFC and ETS) in a peer device. • Detects DCB mis-configuration in a peer device; that is, when DCB features are not compatibly configured on a peer device and the local switch. Mis-configuration detection is feature-specific because some DCB features support asymmetric configuration. • Reconfigures a peer device with the DCB configuration from its configuration source if the peer device is willing to accept configuration. 262 Data Center Bridging (DCB)