58Uplink Failure Detection (UFD)Uplink failure detection (UFD) provides detection of the loss of upstream connectivity and, if used with network interface controller(NIC) teaming, automatic recovery from a failed link.Feature DescriptionA switch provides upstream connectivity for devices, such as servers. If a switch loses its upstream connectivity, downstreamdevices also lose their connectivity. However, the devices do not receive a direct indication that upstream connectivity is lostbecause connectivity to the switch is still operational.UFD allows a switch to associate downstream interfaces with upstream interfaces. When upstream connectivity fails, the switchdisables the downstream links. Failures on the downstream links allow downstream devices to recognize the loss of upstreamconnectivity.For example, as shown in the following illustration, 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 flows from the server to S1and 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 its network traffic, but thetraffic is not successfully switched through S1 because the upstream link is down.• In Step C, UFD on S1 disables the link to the server. The server then stops using the link to S1 and switches to using its link to S2to send traffic upstream to R1.Uplink Failure Detection (UFD) 877
