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 theconfigured 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 theapplication priority TLV received on the configuration-source port. When an applicationpriority 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 receivedapplication priority. Otherwise, these ports use their locally configured PFC priorities inapplication priority TLVs.– If no configuration source is configured, auto-upstream and auto-downstream ports checkto see that the locally configured PFC priorities match the priorities in a received applicationpriority TLV.• On manual ports, an application priority TLV is advertised only if the priorities in the TLV matchthe PFC priorities configured on the port.DCB Configuration ExchangeThe DCBx protocol supports the exchange and propagation of configuration information for theenhanced 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 portwithout requiring that a peer port and the local port use the same configuredvalues for the configurations to be compatible. For example, ETS uses anasymmetric exchange of parameters between DCBx peers.Symmetric DCB parameters are exchanged between a DCBx-enabled port and a peer port butrequires that each configured parameter value be the same for the configurationsin order to be compatible. For example, PFC uses an symmetric exchange ofparameters between DCBx peers.Configuration Source ElectionWhen an auto-upstream or auto-downstream port receives a DCB configuration from a peer, the portfirst 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 localport 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 loggedand the DCBx frame error counter is incremented. Although DCBx is operationally disabled, the portkeeps the peer link up and continues to exchange DCBx packets. If a compatible peer configuration islater received, DCBx is enabled on the port.• If there is no configuration source, a port may elect itself as the configuration source. A port maybecome the configuration source if the following conditions exist:– No other port is the configuration source.– The port role is auto-upstream.– The port is enabled with link up and DCBx enabled.– The port has performed a DCBx exchange with a DCBx peer.264 Data Center Bridging (DCB)
