UplinkFast
UplinkFast is for speeding convergence when a direct link to an upstream
switch fails. The switch identifies backup ports for the root port (these are
called an uplink group). If the root port fails, then one of the ports in the
uplink group is unblocked and transitions immediately to forwarding—it
bypasses the listening and learning stages. It should be used in wiring closet
switches with at least one blocked port.
The command to enable uplinkfast is shown below. Please note that uplinkfast is
enabled globally, so the command affects all ports and all VLANs.
(config)# spanning-tree uplinkfast
BackboneFast
BackboneFast is used for speeding convergence when a link fails that is not
directly connected to the switch. It helps the switch detect indirect failures. If
a switch running BackboneFast receives an inferior BPDU from its designated
bridge, it knows a link on the path to the root has failed. (An inferior BPDU
is one that lists the same switch for root bridge and designated bridge.)
The switch then tries to find an alternate path to the root by sending a Root
Link Query (RLQ) frame out all alternate ports. The root then responds with
an RLQ response, and the port receiving this response can transition to
forwarding. Alternate ports are determined in this way:
■ If the inferior BPDU was received on a blocked port, then the root port
and any other blocked ports are considered alternates.
■ If the inferior BPDU was received on the root port, then all blocked
ports are considered alternates.
■ If the inferior BPDU was received on the root port and there are no
blocked ports, the switch assumes it has lost connectivity with the root
and advertises itself as root.
Configure this command on all switches in the network:
(config)#spanning-tree backbonefast