Concept Guide

not stored in the switch’s running conguration. On a DCBx port that is the conguration source, all PFC and
application priority TLVs are enabled. ETS recommend TLVs are disabled and ETS conguration TLVs are enabled.
Manual The port is congured to operate only with administrator-congured settings and does not auto-congure with
DCB settings received from a DCBx peer or from an internally propagated conguration from the conguration
source. If you enable DCBx, ports in Manual mode advertise their congurations to peer devices but do not accept
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
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Data Center Bridging (DCB)