Reference Guide

62 | Data Center Bridging (DCB)
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DCBx Operation
DCBx performs the following operations:
• Discovers DCB configuration (such as PFC and ETS) in a peer device.
• Detects DCB misconfiguration in a peer device; that is, when DCB features are not compatibly
configured on a peer device and the local switch. Misconfiguration detection is feature-specific
because some DCB features support asymmetric configuration.
• Reconfigures a peer device with the DCB configuration from its configuration source if the peer
device is willing to accept configuration.
• Accepts the DCB configuration from a peer if a DCBx port is in “willing” mode to accept a peer’s
DCB settings and then internally propagates the received DCB configuration to its peer ports.
DCBx Port Roles
The following DCBx port roles are auto-configured on an Aggregator to propagate DCB configurations
learned from peer DCBx devices internally to other switch ports:
• Auto-upstream: The port advertises its own configuration to DCBx peers and receives its configuration
from DCBx peers (ToR or FCF device). The port also propagates its configuration to other ports on the
switch.
The first auto-upstream that is capable of receiving a peer configuration is elected as the configuration
source. The elected configuration source then internally propagates the configuration to auto-down-
stream ports. A port that receives an internally propagated configuration overwrites its local configura-
tion with the new parameter values.
When an auto-upstream port (besides the configuration source) receives and overwrites its configura-
tion with internally propagated information, one of the following actions is taken:
• If the peer configuration received is compatible with the internally propagated port configuration,
the link with the DCBx peer is enabled.
• If the received peer configuration is not compatible with the currently configured port
configuration, the link with the DCBx peer port is disabled and a syslog message for an
incompatible configuration is generated. The network administrator must then reconfigure the peer
device so that it advertises a compatible DCB configuration.
The configuration received from a DCBx peer or from an internally propagated configuration is not
stored in the switch’s running configuration.
On a DCBx port in an auto-upstream role, the PFC and application priority TLVs are enabled. ETS rec-
ommend TLVs are disabled and ETS configuration TLVs are enabled.
• Auto-downstream - The port advertises its own configuration to DCBx peers but is not willing to
receive remote peer configuration. The port always accepts internally propagated configurations from
a configuration source. An auto-downstream port that receives an internally propagated configuration
overwrites its local configuration with the new parameter values.
When an auto-downstream port receives and overwrites its configuration with internally propagated
information, one of the following actions is taken:
• If the peer configuration received is compatible with the internally propagated port configuration,
the link with the DCBx peer is enabled.