White Papers

Configuration Source Election
When an auto-upstream or auto-downstream port receives a DCB configuration from a peer, the port first checks to see if there
is an active configuration source on the switch.
● If a configuration source already exists, the received peer configuration is checked against the local port configuration. If
the received configuration is compatible, the DCBx marks the port as DCBx-enabled. If the configuration received from the
peer is not compatible, a warning message is logged and the DCBx frame error counter is incremented. Although DCBx
is operationally disabled, the port keeps the peer link up and continues to exchange DCBx packets. If a compatible peer
configuration is later received, DCBx is enabled on the port.
● If there is no configuration source, a port may elect itself as the configuration source. A port may become the configuration
source if the following conditions exist:
○ No other port is the configuration source.
○ The port role is auto-upstream.
○ The port is enabled with link up and DCBx enabled.
○ The port has performed a DCBx exchange with a DCBx peer.
○ The switch is capable of supporting the received DCB configuration values through either a symmetric or asymmetric
parameter exchange.
A newly elected configuration source propagates configuration changes received from a peer to the other auto-configuration
ports. Ports receiving auto-configuration information from the configuration source ignore their current settings and use the
configuration source information.
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:
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 of the DCBx Version
The Aggregator operates in auto-detection mode so that 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).
● 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 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.
Data Center Bridging (DCB)
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