Concept Guide
When an auto-downstream port receives and overwrites its conguration with internally propagated information,
one of the following actions is taken:
• If the peer conguration received is compatible with the internally propagated port conguration, the link with
the DCBx peer is enabled.
• If the received peer conguration is not compatible with the currently congured port conguration, the link
with the DCBx peer port is disabled and a syslog message for an incompatible conguration is generated. The
network administrator must then recongure the peer device so that it advertises a compatible DCB
conguration.
– The internally propagated conguration is not stored in the switch's running conguration.
– On a DCBx port in an auto-downstream role, all PFC, application priority, ETS recommend, and ETS
conguration TLVs are enabled.
Conguration source The port is congured to serve as a source of conguration information on the switch. Peer DCB congurations
received on the port are propagated to other DCBx auto-congured ports. If the peer conguration is compatible
with a port conguration, DCBx is enabled on the port.
On a conguration-source port, the link with a DCBx peer is enabled when the port receives a DCB conguration
that can be internally propagated to other auto-congured ports. The conguration received from a DCBx peer is
not stored in the switch’s running conguration. On a DCBx port that is the conguration source, all PFC and
application priority TLVs are enabled. ETS recommend TLVs are disabled and ETS conguration TLVs are enabled.
Manual The port is congured to operate only with administrator-congured settings and does not auto-congure with
DCB settings received from a DCBx peer or from an internally propagated conguration from the conguration
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 EMC 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:
Data Center Bridging (DCB)
297