So how is this rapid convergence or rapid transition to forwarding state
accomplish in 802.1W or Rapid Spanning Tree .
This is one of the most important features introduced in Rapid Spanning Tree
the difference is that legacy Spanning Tree
in other words, the legacy Spanning Tree algorithm passively waited for the network
to converge before moving a port into the forwarding state.
Achieving faster convergence was a matter of tuning
the conservative default parameters are forward delay and max_age timers.
so in the past, you would try and manipulate these timers to get Spanning Tree
to converge quicker but this often resulted in the sacrificing of network stability.
Rapid Spanning Tree is able to actively confirm that a port can safely transition
to forwarding without relying on any timer configuration.
that’s the big difference it do went rely on timers
there is a negotiation between the switches on point-to-point links
to allow them to converge quicker.
so there’s a feedback mechanism that operates
between Rapid Spanning Tree compliant bridges to achieve faster convergence
you need to configure edge port and links between switches
you need to become point-to-point links.
Now an edge point is essentially the same as Portfast ports
they transition immediately to the forwarding state.
This is to allow end stations to skip the listening
and learning stages in Spanning Tree convergence
an edge port also does not generate topology changes
when its link toggles
so in other words, when a link goes down or comes up
and its configure as an edge port or a Portfast port
it doesn’t cause the network topology to recalculate.
Unlike Portfast through an edge port that receives the BPDU
immediately losses it's edge port status
and becomes normal Spanning Tree port
that is a built-in security mechanism to stop someone accidentally plugging in
a switch or a hub into Portfast port and causing a loop.
In Cisco's implementation, the portfast command is used for edge port configuration
thus making the transition to Rapid Spanning Tree simpler
in a separate video, I'll show you the configuration and testing of Portfast ports.
I’ve already demonstrated how to set up a point-to-point link
this is automatically determined on physical switches using the duplex of a port.
A port operating in full duplex is assumed to be point-to-point
half duplex is considered to be a shared port.
On switch 2 in this topology gigabit 0/0 is a point-to-point link
gigabit 0/1 is a shared port because it's connected to a hub.
it’s a half duplex connection.
In today’s networks, most links are operating in full duplex mode
and are therefore treated as point-point links between switches in Rapid Spanning Tree