Reference Guide

310 | Data Center Bridging (DCB)
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Configuring DCBx Operation
The data center bridging exchange protocol (DCBx) is used by DCB devices to exchange configuration
information with directly connected peers using the link layer discovery protocol (LLDP) protocol. DCBx
can detect the mis-configuration 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:
• Configuring Priority-Based Flow Control
• Configuring Enhanced Transmission Selection
• FIP Snooping
• Chapter 13, Data Center Bridging (DCB)
The following versions of DCBx are supported CIN, CEE, and IEEE2.5.
Prerequisite: DCBx requires the LLDP to be enabled 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.
• Accepts the DCB configuration from a peer if a DCBx port is in “willing” mode to accept a peer’s
DCB settings and then internally propagates the received DCB configuration to its peer ports.
DCBx Port Roles
Use the following DCBx port roles to enable the auto-configuration of DCBx-enabled ports and propagate
DCB configurations learned from peer DCBx devices internally to other switch ports:
• Auto-upstream: The port advertises its own configuration to DCBx peers and is
willing to receive peer
configuration. The port also propagates its configuration to other ports on the switch.
The first auto-upstream that is capable of receiving a peer configuration is elected as the
configuration source. The elected configuration source then internally propagates the configuration
to other auto-upstream and auto-downstream ports. A port that receives an internally propagated
configuration overwrites its local configuration with the new parameter values.