Uplink 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 Description
A switch provides upstream connectivity for devices, such as servers. If a switch loses its upstream connectivity, downstream devices also
lose their connectivity. However, the devices do not receive a direct indication that upstream connectivity is lost because connectivity to
the switch is still operational.
UFD allows a switch to associate downstream interfaces with upstream interfaces. When upstream connectivity fails, the switch disables
the downstream links. Failures on the downstream links allow downstream devices to recognize the loss of upstream connectivity.
For example, as shown in the following illustration, Switches S1 and S2 both have upstream connectivity to Router R1 and downstream
connectivity to the server. UFD operation is shown in Steps A through C:
• In Step A, the server conguration uses the connection to S1 as the primary path. Network trac ows from 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 its network trac, but the trac 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 S2 to
send trac upstream to R1.
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