Spanning Tree PortFast causes an interface configured as a Layer 2
access port to transition from blocking to forwarding state immediately,
bypassing the listening and learning states. You can use PortFast on Layer 2
access ports, which are connected to a single workstation or to a server, to
allow those devices to connect to the network immediately, rather than waiting
for spanning tree to converge. If an interface configured with PortFast
receives a BPDU, then spanning tree can put the port into the blocking state
utilizing a feature called BPDU guard.
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CAUTION:
Because the purpose of PortFast is to minimize the time that access
ports must wait for spanning tree to converge, it should be used only on access
ports. If you enable PortFast on a port connecting to another switch, you risk
creating a spanning tree loop.
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