• If the configuration received from the peer is not compatible with the internally propagated
configuration used by the configuration source, the port is disabled as a client for DCBx operation and
synchronization and a syslog error message is generated. The port keeps the peer link up and
continues to exchange DCBx packets. If a compatible configuration is later received 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 a DCBx port in a manual role. When a configuration source is elected, all auto-
upstream ports other than the configuration source are marked as willing disabled. The internally
propagated DCB configuration is refreshed on all auto-configuration ports and each port may begin
configuration negotiation with a DCBx peer again.
Auto-Detection and Manual Configuration of the DCBx Version
When operating in Auto-Detection mode (the DCBx version auto command), a DCBx port
automatically detects the DCBx version 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 with the 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 in the Configuring DCBx), DCBx operations are performed according to the
configured version, including fast and slow transmit timers and message formats. If a DCBx frame with a
different version is received, a syslog message is generated and the peer version is recorded 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 is configured to operate in CEE mode and vice versa. In this case, the unrecognized
TLVs cause the unrecognized TLV counter 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 and acknowledge the number sent in the DCBx control TLVs.
DCBx Example
The following figure shows how DCBX is used on an MXL Switch installed in a PowerEdge M1000e
chassis in which servers are also installed.
The external 40GbE ports on the base module (ports 33 and 37) of two switches are used for uplinks
configured as DCBx auto-upstream ports. The MXL switch is connected to third-party, top-of-rack (ToR)
switches through 40GbE uplinks. The ToR switches are part of a Fibre Channel storage network.
The internal ports (ports 1-32) connected to the 10GbE backplane are configured as auto-downstream
ports.
Data Center Bridging (DCB) 277