– The switch is capable of supporting the received DCB configuration values through either a symmetric or asymmetricparameter exchange.A newly elected configuration source propagates configuration changes received from a peer to the other auto-configuration ports.Ports receiving auto-configuration information from the configuration source ignore their current settings and use the configurationsource information.Propagation of DCB InformationWhen an auto-upstream or auto-downstream port receives a DCB configuration from a peer, the port acts as a DCBx client andchecks if a DCBx configuration source exists on the switch.• If a configuration source is found, the received configuration is checked against the currently configured values that are internallypropagated by the configuration source. If the local configuration is compatible with the received configuration, the port isenabled for DCBx operation and synchronization.• If the configuration received from the peer is not compatible with the internally propagated configuration used by theconfiguration source, the port is disabled as a client for DCBx operation and synchronization and a syslog error message isgenerated. The port keeps the peer link up and continues to exchange DCBx packets. If a compatible configuration is laterreceived from the peer, the port is enabled for DCBx operation.NOTE: DCB configurations internally propagated from a configuration source do not overwrite the configuration on aDCBx port in a manual role. When a configuration source is elected, all auto-upstream ports other than the configurationsource are marked aswilling disabled. The internally propagated DCB configuration is refreshed on all auto-configurationports and each port may begin configuration negotiation with a DCBx peer again.Auto-Detection and Manual Configuration of the DCBx VersionWhen operating in Auto-Detection mode (the DCBx version auto command), a DCBx port automatically detects the DCBxversion on a peer port. Legacy CIN and CEE versions are supported in addition to the standard IEEE version 2.5 DCBx.A DCBx port detects a peer version after receiving a valid frame for that version. The local DCBx port reconfigures to operate withthe peer version and maintains the peer version on the link until one of the following conditions occurs:• The switch reboots.• The link is reset (goes down and up).• User-configured CLI commands require the version negotiation to restart.• The peer times out.• Multiple peers are detected on the link.If you configure a DCBx port to operate with a specific version (the DCBx version {cee | cin | ieee-v2.5} command inthe Configuring DCBx), DCBx operations are performed according to the configured version, including fast and slow transmit timersand message formats. If a DCBx frame with a different version is received, a syslog message is generated and the peer version isrecorded in the peer status table. If the frame cannot be processed, it is discarded and the discard counter is incremented.NOTE: Because DCBx TLV processing is best effort, it is possible that CIN frames may be processed when DCBx isconfigured to operate in CEE mode and vice versa. In this case, the unrecognized TLVs cause the unrecognized TLVcounter to increment, but the frame is processed and is not discarded.Legacy DCBx (CIN and CEE) supports the DCBx control state machine that is defined to maintain the sequence number andacknowledge the number sent in the DCBx control TLVs.DCBx ExampleThe following figure shows how to use DCBx.The external 40GbE 40GbE ports on the base module (ports 33 and 37) of two switches are used for uplinks configured as DCBxauto-upstream ports. The device is connected to third-party, top-of-rack (ToR) switches through 40GbE uplinks. The ToR switchesare part of a Fibre Channel storage network.The internal ports (ports 1-32) connected to the 10GbE backplane are configured as auto-downstream ports.262 Data Center Bridging (DCB)
