Concept Guide

Auto-Detection and Manual Conguration 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 recongures 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-congured CLI commands require the version negotiation to restart.
• The peer times out.
• Multiple peers are detected on the link.
If you congure a DCBx port to operate with a specic version (the DCBx version {cee | cin | ieee-v2.5} command in the
Conguring DCBx), DCBx operations are performed according to the congured version, including fast and slow transmit timers and
message formats. If a DCBx frame with a dierent 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 eort, it is possible that CIN frames may be processed when DCBx is congured 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 dened to maintain the sequence number and acknowledge
the number sent in the DCBx control TLVs.
DCBx Example
The following gure 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 congured as DCBx auto-
upstream ports. The device 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 congured as auto-downstream ports.
On the S4048, PFC and ETS use DCBx to exchange link-level conguration with DCBx peer devices.
Data Center Bridging (DCB)
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