Users Guide

Applying DCB Policies in a Switch Stack
You can apply DCB policies with PFC and ETS congurations 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 specied 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
Congure a DCBx Operation
DCB devices use data center bridging exchange protocol (DCBx) to exchange conguration information with directly connected
peers using the link layer discovery protocol (LLDP) protocol.
DCBx can detect the misconguration of a peer DCB device, and optionally, congure 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 ow control (PFC) and enhanced trac selection (ETS), to
exchange link-level congurations in a converged Ethernet environment. DCBx is also deployed in topologies that support lossless
operation for FCoE or iSCSI trac. 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:
• Congure 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 conguration (such as PFC and ETS) in a peer device.
• Detects DCB mis-conguration in a peer device; that is, when DCB features are not compatibly congured on a peer device and
the local switch. Mis-conguration detection is feature-specic because some DCB features support asymmetric conguration.
• Recongures a peer device with the DCB conguration from its conguration source if the peer device is willing to accept
conguration.
• Accepts the DCB conguration 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 conguration to its peer ports.
DCBx Port Roles
To enable the auto-conguration of DCBx-enabled ports and propagate DCB congurations learned from peer DCBx devices
internally to other switch ports, use the following DCBx port roles.
Auto-upstream
The port advertises its own conguration to DCBx peers and is willing to receive peer conguration. The
port also propagates its conguration to other ports on the switch.
The rst auto-upstream that is capable of receiving a peer conguration is elected as the conguration
source. The elected conguration source then internally propagates the conguration to other auto-
upstream and auto-downstream ports. A port that receives an internally propagated conguration
overwrites its local conguration with the new parameter values. When an auto-upstream port (besides the
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Data Center Bridging (DCB)