118 | Data Center Bridging (DCB)
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Enabling Data Center Bridging
Data center bridging is enabled by default on an MXL 10/40GbE Switch to support converged enhanced
Ethernet (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) snooping
DCB processes virtual local area network (VLAN)-tagged packets and dot1p priority values. Untagged
packets 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 it
maps to different data queues. The dot1p-queue assignments used on an MXL Switch is shown in
Table 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 traffic
handling for PFC. Disabling DCB does not release the buffers reserved by default. To utilize reserved
buffers for non-DCB applications, you have to explicitly release the buffers (Refer to Configuring the PFC
Buffer in a Switch Stack).
To disable or re-enable DCB on a switch, enter the following commands:
Task Command Command Mode
Disable DCB.
no dcb enable
CONFIGURATION
Re-enable DCB.
dcb enable
CONFIGURATION
FTOS Behavior:
DCB is not supported if you enable link-level flow control on one or more interfaces (refer to Layer 2
Flow Control Using Ethernet Pause Frames on page 247).
After you disable DCB, if link-level flow control is not automatically enabled on an interface, manually
shut down the interface (shutdown command) and re-enable it (no shutdown command) to enable flow
control.
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