Dcb Configuration Exchange; Configuration Source Election - Dell S4820T Configuration Manual

On a DCBx port in a manual role, all PFC, application priority, ETS recommend, and
ETS configuration TLVs are enabled.
When making a configuration change to a DCBx port in a Manual role, Dell
Networking recommends shutting down the interface using the shutdown
command, change the configuration, 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
configured PFC priorities on the port.
• On auto-upstream and auto-downstream ports:
– If a configuration source is elected, the ports send an application priority TLV based on the
application priority TLV received on the configuration-source port. When an application
priority TLV is received on the configuration-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 configured PFC priorities in
application priority TLVs.
– If no configuration source is configured, auto-upstream and auto-downstream ports check
to see that the locally configured 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 configured on the port.

DCB Configuration Exchange

The DCBx protocol supports the exchange and propagation of configuration information for the
enhanced transmission selection (ETS) and priority-based flow control (PFC) DCB features.
DCBx uses the following methods to exchange DCB configuration 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 configured
values for the configurations 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 configured parameter value be the same for the configurations
in order to be compatible. For example, PFC uses an symmetric exchange of
parameters between DCBx peers.

Configuration Source Election

When an auto-upstream or auto-downstream port receives a DCB configuration from a peer, the port
first checks to see if there is an active configuration source on the switch.
• If a configuration source already exists, the received peer configuration is checked against the local
port configuration. If the received configuration is compatible, the DCBx marks the port as DCBx-
enabled. If the configuration 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
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Data Center Bridging (DCB)