Concept Guide

or propagate internal or external congurations. Unlike other user-congured ports, the conguration of DCBx
ports in Manual mode is saved in the running conguration.
On a DCBx port in a manual role, all PFC, application priority, ETS recommend, and ETS conguration TLVs are
enabled.
When making a conguration change to a DCBx port in a Manual role, Dell EMC Networking recommends shutting
down the interface using the shutdown command, change the conguration, then re-activate the interface using
the no shutdown command.
The default for the DCBx port role is manual.
NOTE: On a DCBx port, application priority TLV advertisements are handled as follows:
• The application priority TLV is transmitted only if the priorities in the advertisement match the congured PFC priorities on the
port.
• On auto-upstream and auto-downstream ports:
– If a conguration source is elected, the ports send an application priority TLV based on the application priority TLV received on
the conguration-source port. When an application priority TLV is received on the conguration-source port, the auto-
upstream and auto-downstream ports use the internally propagated PFC priorities to match against the received application
priority. Otherwise, these ports use their locally congured PFC priorities in application priority TLVs.
– If no conguration source is congured, auto-upstream and auto-downstream ports check to see that the locally congured
PFC priorities match the priorities in a received application priority TLV.
• On manual ports, an application priority TLV is advertised only if the priorities in the TLV match the PFC priorities congured on the
port.
DCB Conguration Exchange
The DCBx protocol supports the exchange and propagation of conguration information for the enhanced transmission selection (ETS) and
priority-based ow control (PFC) DCB features.
DCBx uses the following methods to exchange DCB conguration parameters:
Asymmetric
DCB parameters are exchanged between a DCBx-enabled port and a peer port without requiring that a peer port
and the local port use the same congured values for the congurations to be compatible. For example, ETS uses
an asymmetric exchange of parameters between DCBx peers.
Symmetric DCB parameters are exchanged between a DCBx-enabled port and a peer port but requires that each congured
parameter value be the same for the congurations in order to be compatible. For example, PFC uses an
symmetric exchange of parameters between DCBx peers.
Conguration Source Election
When an auto-upstream or auto-downstream port receives a DCB conguration from a peer, the port rst checks to see if there is an
active conguration source on the switch.
• If a conguration source already exists, the received peer conguration is checked against the local port conguration. If the received
conguration is compatible, the DCBx marks the port as DCBx-enabled. If the conguration received from the peer is not compatible, a
warning message is logged and the DCBx frame error counter is incremented. Although DCBx is operationally disabled, the port keeps
the peer link up and continues to exchange DCBx packets. If a compatible peer conguration is later received, DCBx is enabled on the
port.
• If there is no conguration source, a port may elect itself as the conguration source. A port may become the conguration source if
the following conditions exist:
– No other port is the conguration source.
– The port role is auto-upstream.
Data Center Bridging (DCB)
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