Data Center Bridging (DCB) | 67Auto-Detection of the DCBX VersionThe Aggregator operates in auto-detection mode so that a DCBX port automatically detects the DCBXversion on a peer port. Legacy CIN and CEE versions are supported in addition to the standard IEEEversion 2.5 DCBX.A DCBX port detects a peer version after receiving a valid frame for that version. The local DCBX portreconfigures to operate with the peer version and maintains the peer version on the link until one of thefollowing conditions occurs:• The switch reboots.• The link is reset (goes down and up).• The peer times out.• Multiple peers are detected on the link.DCBX operations on a port are performed according to the auto-configured DCBX version, including fastand slow transmit timers and message formats. If a DCBX frame with a different version is received, asyslog message is generated and the peer version is recorded in the peer status table. If the frame cannot beprocessed, it is discarded and the discard counter is incremented.DCBX ExampleFigure 6-7 shows how DCBX is used on an Aggregator installed in a PowerEdge M1000e chassis in whichservers are also installed.• The external 40GbE ports on the base module (ports 33 and 37) of two switches are used for uplinksconfigured as DCBX auto-upstream ports. The Aggregator is connected to third-party, top-of-rack(ToR) switches through 40GbE uplinks. The ToR switches are part of a Fibre Channel storagenetwork.• The internal ports (ports 1-32) connected to the 10GbE backplane are configured as auto-downstreamports.• On the Aggregator, PFC and ETS use DCBX to exchange link-level configuration with DCBX peerdevices.
