Data Center Bridging (DCB) | 135Configuration Source ElectionWhen an auto-upstream or auto-downstream port receives a DCB configuration from a peer, the port firstchecks 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 asDCBX-enabled. If the configuration received from the peer is not compatible, a warning message islogged 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 peerconfiguration is later 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.• The switch is capable of supporting the received DCB configuration values through either asymmetric or asymmetric parameter exchange.A newly elected configuration source propagates configuration changes received from a peer to the otherauto-configuration ports. Ports receiving auto-configuration information from the configuration sourceignore their current settings and use the configuration source information.Propagation of DCB InformationWhen an auto-upstream or auto-downstream port receives a DCB configuration from a peer, the port actsas a DCBX client and checks if a DCBX configuration source exists on the switch.• If a configuration source is found, the received configuration is checked against the currentlyconfigured values that are internally propagated by the configuration source. If the local configurationis compatible with the received configuration, the port is enabled for DCBX operation andsynchronization.• If the configuration received from the peer is not compatible with the internally propagatedconfiguration used by the configuration source, the port is disabled as a client for DCBX operation andsynchronization and a syslog error message is generated. The port keeps the peer link up and continuesto exchange DCBX packets. If a compatible configuration is later received from the peer, the port isenabled for DCBX operation.Note: DCB configurations internally propagated from a configuration source do not overwrite theconfiguration on a DCBX port in a manual role.When a configuration source is elected, all auto-upstream ports other than the configuration source aremarked as willing disabled. The internally propagated DCB configuration is refreshed on allauto-configuration ports and each port may begin configuration negotiation with a DCBX peer again.
