Users Guide

Propagation of DCB Information
When an auto-upstream or auto-downstream port receives a DCB configuration from a peer, the port acts as a DCBx client and checks 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 internally
propagated by the configuration source. If the local configuration is compatible with the received configuration, the port is enabled for
DCBx operation and synchronization.
• 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 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 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 configured as auto-downstream ports.
On the S4048, PFC and ETS use DCBx to exchange link-level configuration with DCBx peer devices.
Data Center Bridging (DCB)
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