Administrator Guide

DCB Configuration Exchange
The DCBx protocol supports the exchange and propagation of configuration information for the enhanced
transmission selection (ETS) and priority-based flow control (PFC) DCB features.
DCBx uses the following methods to exchange DCB configuration parameters:
Asymmetric DCB parameters are exchanged between a DCBx-enabled port and a peer port without
requiring that a peer port and the local port use the same configured values for the
configurations to be compatible. For example, ETS uses an asymmetric exchange of
parameters between DCBx peers.
Symmetric DCB parameters are exchanged between a DCBx-enabled port and a peer port but
requires that each configured parameter value be the same for the configurations in
order to be compatible. For example, PFC uses an symmetric exchange of parameters
between DCBx peers.
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.
FC Flex IO Modules 1069