Dell Force10 MXL Blade - Auto-Detection and Manual Configuration of the DCBX Version; DCBX Example

136 | Data Center Bridging (DCB)
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Auto-Detection and Manual Configuration of the DCBX
Version
When operating in Auto-Detection mode (dcbx version auto command in DCBX Configuration
Procedure), 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 (dcbx version {cee | cin | ieee-v2.5}
command in DCBX Configuration Procedure), 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.
Legacy DCBX (CIN and CEE) supports the DCBX control state machine that is defined to maintain the
sequence number and acknowledge number sent in the DCBX control TLVs.
DCBX Example
Figure 8-4 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.
• On the MXL Switch, PFC and ETS use DCBX to exchange link-level configuration with DCBX peer
devices.
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 be incremented, but the frame is processed and is not discarded.