Administrator Guide

The internally propagated configuration is not stored in the switch’s running
configuration. On a DCBx port in an auto-downstream role, all PFC, application priority,
ETS recommend, and ETS configuration TLVs are enabled.
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: You can change the port roles only in the PMUX mode. Use the following command to change the
port roles:
dcbx port-role {auto-downstream | auto-upstream | config-source | manual}
manual is the default port 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.
Data Center Bridging (DCB) 294