Original subtitles

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So how is this rapid convergence or rapid transition to forwarding state

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accomplish in 802.1W or Rapid Spanning Tree .

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This is one of the most important features introduced in Rapid Spanning Tree

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the difference is that legacy Spanning Tree

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in other words, the legacy Spanning Tree algorithm passively waited for the network

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to converge before moving a port into the forwarding state.

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Achieving faster convergence was a matter of tuning

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the conservative default parameters are forward delay and max_age timers.

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so in the past, you would try and manipulate these timers to get Spanning Tree

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to converge quicker but this often resulted in the sacrificing of network stability.

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Rapid Spanning Tree is able to actively confirm that a port can safely transition

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to forwarding without relying on any timer configuration.

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that’s the big difference it do went rely on timers

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there is a negotiation between the switches on point-to-point links

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to allow them to converge quicker.

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so there’s a feedback mechanism that operates

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between Rapid Spanning Tree compliant bridges to achieve faster convergence

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you need to configure edge port and links between switches

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you need to become point-to-point links.

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Now an edge point is essentially the same as Portfast ports

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they transition immediately to the forwarding state.

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This is to allow end stations to skip the listening

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and learning stages in Spanning Tree convergence

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an edge port also does not generate topology changes

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when its link toggles

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so in other words, when a link goes down or comes up

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and its configure as an edge port or a Portfast port

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it doesn’t cause the network topology to recalculate.

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Unlike Portfast through an edge port that receives the BPDU

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immediately losses it's edge port status

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and becomes normal Spanning Tree port

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that is a built-in security mechanism to stop someone accidentally plugging in

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a switch or a hub into Portfast port and causing a loop.

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In Cisco's implementation, the portfast command is used for edge port configuration

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thus making the transition to Rapid Spanning Tree simpler

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in a separate video, I'll show you the configuration and testing of Portfast ports.

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I’ve already demonstrated how to set up a point-to-point link

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this is automatically determined on physical switches using the duplex of a port.

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A port operating in full duplex is assumed to be point-to-point

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half duplex is considered to be a shared port.

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On switch 2 in this topology gigabit 0/0 is a point-to-point link

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gigabit 0/1 is a shared port because it's connected to a hub.

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it’s a half duplex connection.

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In today’s networks, most links are operating in full duplex mode

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and are therefore treated as point-point links between switches in Rapid Spanning Tree