Dcb Configuration Exchange; Configuration Source Election - Dell S4048–ON Configuration Manual

devices but do not accept or propagate internal or external configurations. Unlike other user-configured
ports, the configuration of DCBx ports in Manual mode is saved in the running configuration.
On a DCBx port in a manual role, all PFC, application priority, ETS recommend, and ETS configuration TLVs
are enabled.
When making a configuration change to a DCBx port in a Manual role, Dell Networking recommends
shutting down the interface using the shutdown command, change the configuration, then re-activate the
interface using the no shutdown command.
The default for the DCBx port role is manual.
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

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.
Data Center Bridging (DCB)
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