Users Guide
source. If you enable DCBx, ports in Manual mode advertise their congurations to peer devices but do not accept
or propagate internal or external congurations. Unlike other user-congured ports, the conguration of DCBx
ports in Manual mode is saved in the running conguration.
On a DCBx port in a manual role, all PFC, application priority, ETS recommend, and ETS conguration TLVs are
enabled.
When making a conguration change to a DCBx port in a Manual role, Dell Networking recommends shutting down
the interface using the shutdown command, change the conguration, 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 congured PFC priorities on the
port.
• On auto-upstream and auto-downstream ports:
– If a conguration source is elected, the ports send an application priority TLV based on the application priority TLV received on
the conguration-source port. When an application priority TLV is received on the conguration-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 congured PFC priorities in application priority TLVs.
– If no conguration source is congured, auto-upstream and auto-downstream ports check to see that the locally congured
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 congured on the
port.
DCB Conguration Exchange
The DCBx protocol supports the exchange and propagation of conguration information for the enhanced transmission selection (ETS) and
priority-based ow control (PFC) DCB features.
DCBx uses the following methods to exchange DCB conguration 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 congured values for the congurations 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 congured
parameter value be the same for the congurations in order to be compatible. For example, PFC uses an
symmetric exchange of parameters between DCBx peers.
Conguration Source Election
When an auto-upstream or auto-downstream port receives a DCB conguration from a peer, the port rst checks to see if there is an
active conguration source on the switch.
• If a conguration source already exists, the received peer conguration is checked against the local port conguration. If the received
conguration is compatible, the DCBx marks the port as DCBx-enabled. If the conguration 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 conguration is later received, DCBx is enabled on the
port.
• If there is no conguration source, a port may elect itself as the conguration source. A port may become the conguration source if
the following conditions exist:
– No other port is the conguration source.
Data Center Bridging (DCB)
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