Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.112.1P1 - Page 264

source. If you enable DCBx, ports in Manual mode advertise their configurations to peer 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 Symmetric 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. 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. 264 Data Center Bridging (DCB)