BackboneFast - Fast convergence of Network backbone after STP topology change. An indirectly connected switch can detect a link failure by receiving inferior BPDU's from its designated bridge, root port or blocked port. Normally these BPDU's would be ignored by the maximum aging time.
The switch determines if it has an alternate path to the root bridge, if so the root port and other blocked ports become alternate paths to root bridge. If the inferior BPDU is noticed on the root port, all blocked ports become an alternate path to root bridge. If by chance there are no blocked ports and inferior BPDU's are received on the root port becomes the root switch and bypasses max aging time on root.
If the switch has an alternative path to root Bridge, a Root Link Query PDU is transmitted on all alternate paths to the root bridge, if no alternate is found the max aging time on inferior BPDU ports expire and be, the same applies if alternate paths to root bridge lose connectivity. If paths still exist to root bridge, all ports which received BPDU's become designated ports through listening and learning, then forwarding.
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