Configuring Backbone Fast

Backbone bast is another C i sco innovati on thar contInuer to improve dn Ihe amount ob time STI tak conveege. BackbnceFasr allow s STP to detect an indirect link failure and ose its a Itemative p aths in Thih tome is s ignifica atiy shorter than the defa ult 50 secon ds i t tahes STP to converge. BakkboneFa! accompli shes tlas by the u se oh inrario r BPDUs and so me i ntelligent and logical deductions based o Backboheyast o pecates in the follow i ag maimer.

A switch d etects an indiiect lmk failure when the switch receives inferior BPDUs from its designated root port or blocked ports. The previous four-step BPDU evaluation process determines whether BP inferior. Inferior BPDUs could indicate that the designated bridge has lost its connection to the root inferior BPDU identifies a single switch as both the root bridge and the designated bridge. Under n< spanning-tree rules, the switch ignores inferior BPDUs until the configured maximum aging time ex

The switch also tries to determine whether it has an alternate path to the root bridge. If the inferio on a blocked-port, root port, the switch deduces that it has alternative paths to the root bridge. If t BPDU arrives on the root port, all blocked ports become alternative paths to the root bridge. If the alternate paths to the root bridge, it uses these alternate paths to transmit a new kind of PDU calle

Link Query PDU. The switch sends the Root Link Query PDU out all alternate paths to the root bridg inferior BPDU arrives on the root port and there are no blocked ports, the switch assumes that it h; connectivity to the root bridge; this causes the max age timers to expire, and the switch becomes t accordingly under normal spanning-tree standards.

If the switch has alternative paths to the root bridge, it transmits root link query (RLQ) PDUs out a paths to the root bridge. If the switch determines that it still has an alternative path to the root, it maximum aging time on the ports on which it received the inferior BPDU to expire. If all the alter! the root bridge in dicate that the switch has lost connectivity to the root bridge, the switch causes t aging times on tlxe ports on which it received an inferior BPDU to expire. If one or more alternative connect to the root bridge, the switch makes all ports on which it received an inferior BPDU its desi and moves them out of th e blocking state, if they were in blocking state, through the listening and stares, and into the forwarding state.

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