118 | 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 mEnabling Data Center BridgingData center bridging is enabled by default on an MXL 10/40GbE Switch to support converged enhancedEthernet (CEE) in a data center network, and is a prerequisite for configuring:• Priority-based flow control• Enhanced transmission selection• Data center bridging exchange protocol• FCoE initialization protocol (FIP) snoopingDCB processes virtual local area network (VLAN)-tagged packets and dot1p priority values. Untaggedpackets are treated with a dot1p priority of 0.For DCB to operate effectively, you can classify ingress traffic according to its dot1p priority so that itmaps to different data queues. The dot1p-queue assignments used on an MXL Switch is shown inTable 8-1 in QoS dot1p Traffic Classification and Queue Assignment.On the MXL Switch, by default, DCB is enabled and MMU buffers are reserved to achieve no-drop traffichandling for PFC. Disabling DCB does not release the buffers reserved by default. To utilize reservedbuffers for non-DCB applications, you have to explicitly release the buffers (Refer to Configuring the PFCBuffer in a Switch Stack).To disable or re-enable DCB on a switch, enter the following commands:Task Command Command ModeDisable DCB. no dcb enable CONFIGURATIONRe-enable DCB. dcb enable CONFIGURATIONFTOS Behavior:DCB is not supported if you enable link-level flow control on one or more interfaces (refer to Layer 2Flow Control Using Ethernet Pause Frames on page 247).After you disable DCB, if link-level flow control is not automatically enabled on an interface, manuallyshut down the interface (shutdown command) and re-enable it (no shutdown command) to enable flowcontrol.
