Uplink Failure Detection (UFD) | 23120Uplink Failure Detection (UFD)Uplink failure detection (UFD) is enabled by default on the Aggregator.UFD provides detection of the loss of upstream connectivity and, if used with NIC teaming, automaticrecovery from a failed link.An Aggregator auto-configures with UFD enabled. You can use CLI commands to display the status andconfiguration of uplink-state groups, and enable UFD debugging.Feature DescriptionA switch provides upstream connectivity for devices, such as servers. If a switch loses its upstreamconnectivity, downstream devices also lose their connectivity. However, the devices do not receive a directindication that upstream connectivity is lost since connectivity to the switch is still operational.UFD allows a switch to associate downstream interfaces with upstream interfaces. When upstreamconnectivity fails, the switch disables the downstream links. Failures on the downstream links allowdownstream devices to recognize the loss of upstream connectivity.For example, in Figure 20-1 Switches S1 and S2 both have upstream connectivity to Router R1 anddownstream connectivity to the server. UFD operation is shown in Steps A through C:• In Step A, the server configuration uses the connection to S1 as the primary path. Network traffic flowsfrom the server to S1 and then upstream to R1.• In Step B, the upstream link between S1 and R1 fails. The server continues to use the link to S1 for itsnetwork traffic, but the traffic is not successfully switched through S1 because the upstream link isdown.• In Step C, UFD on S1 disables the link to the server. The server then stops using the link to S1 andswitches to using its link to S2 to send traffic upstream to R1.Note: Uplink failure detection is also referred to as link tracking.
