Reference Guide

Default DCBX port role: Uplink ports are auto-configured in an auto-upstream role. Server-facing ports

are auto-configured in an auto-downstream role.

NOTE: On a DCBx port, application priority TLV advertisements are handled as follows:

• The application priority TLV is transmitted only if the priorities in the advertisement match the

configured PFC priorities on the port.

• On auto-upstream and auto-downstream ports:

– If a configuration source is elected, the ports send an application priority TLV based on the

application priority TLV received on the configuration-source port. When an application

priority TLV is received on the configuration-source port, the auto-upstream and auto-

downstream ports use the internally propagated PFC priorities to match against the received

application priority. Otherwise, these ports use their locally configured PFC priorities in

application priority TLVs.

– If no configuration source is configured, auto-upstream and auto-downstream ports check

to see that the locally configured PFC priorities match the priorities in a received application

priority TLV.

• On manual ports, an application priority TLV is advertised only if the priorities in the TLV match

the PFC priorities configured on the port.

DCB Configuration Exchange

On an Aggregator, the DCBX protocol supports the exchange and propagation of configuration

information for the following DCB features.

• Enhanced transmission selection (ETS)

• Priority-based flow control (PFC)

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:

Data Center Bridging (DCB)