So let's look at rapid spending tree protocol or ADA 2.1 w.
This is an evolution of the triple e ada 2.1 D standard.
However, rapid spanning tree provides rapid failover and convergence times.
The big difference that you need to remember here is that rapid spending tree is not based on timers
like Ed or one RD, so it offers a improvement over the 32nd interval or longer that ed to one D takes
to move a port to the forwarding state.
What rapid spending tree does is it uses a bridge to bridge handshake mechanism, which allows ports
to move directly to forwarding rather than waiting for the port.
To move from listening to learning to forwarding.
It is backward compatible with ADA 2 to 1 DD is transparent to end users and is standards based, but
it does introduce some enhancements, including new port roll assignments and port states.
A new BPD new format and BPD new processing.
A bridge to bridge handshake mechanism and different topology change notifications and processing procedures.
It's what our port states and port roles in 82 to 1 D and rapid spending tree.
There are only three port states in rapid spending tree learning, forwarding and discarding.
In ed one d we had disabled blocking and listening, and these have been merged into the discarding
state.
So when you administratively disable a port that's called disabled in eight or one D, but it's called
discarding in inherited to one W or rapid spending tree, a blocking port that does not forward user
data frames and ignores incoming data frames is called discarding an editor to 1wa listening port is
not used and edited a1wa learning port is known as a learning port and a forwarding port is known as
a forwarding port in 82 to 1.
W So we have learning, forwarding and discarding disabled blocking and listening have been merged into
the discarding state.
In editor to one w Cisco still uses the term blocking for discarding.
So just see those terms as interchangeable terms.
Blocking is discarding and discarding is blocking.
So what about port roles?
The role is now a variable assigned to a given port.
Previously we had root ports and designated ports and those remain.
But blocking ports are now split into what are called backup and alternate port roles.
Spanning three will determine the role of the port by looking at the BPD use received and deciding which
one is more useful than another.
A more useful BPD view is a BPD view that has a lower path cost or a better path to get to the root
bridge.
So let's start with a route put.
With the spending tree protocol.
The spending tree algorithm elects a single route bridge for the entire bridge network.
Now with PVS DT.
That's done on a per VLAN basis, but in ADA 2 to 1 DX or rapid spanning tree, there's only one route
bridge or route switch for the entire layer two topology.
The Route Bridge sends BP to use at a more useful than the ones sent by any other bridge.
The port receiving the best BP due on a bridge or switch is known as the root port.
In other words, this is the port that is closest to the Route Bridge in terms of path cost.
So in this topology, if this switches the root switch, this port would be the root port of switch
A and this would be the root port of switch B.
The Route Bridge doesn't have a route port.
All other bridges have at least one root port.
What is a designated port.
This is the best port on a segment to use to get to the root bridge.
So all bridges connected to a given segment, listen to each other's BPD use and agree on the bridge,
sending the best BPD view as the designated bridge for the segment.
So in this topology, this switches the route.
So for this segment, this is the designated port or best port to use to get to the Route Bridge.
On this segment, this is the best port to use to get to the route bridge.
So this is the designated port.
Once again, just imagine that you've got a PC connected to the middle of this cable, which is the
best way to get to the Route Bridge this way or this way.
And as we can see, this is the best path or best way to get to the route bridge.
So this is the route port.
It's much quicker to go this way than it is to go this way.
So this is the designated port on this segment.
Let's assume that we've got a hub connected here.
This port has been chosen as the designated port, and that may be because the switch here has a lower
bridge ID than switch A and this is port one, which is lower than port two.
So this is the designated port on that segment.
Now what about alternate and backup patrols?
These correspond to the blocking state in 2 to 1 D.
A blocked port is defined as any port that is not a designated or route port.
A port remains blocked as long as it receives more useful.
In other words, better BPT use than the one it would send out on the segment.
Therefore, Port must receive BPD use in order to stay blocked.
If it doesn't receive BPD use, it will transition to the forwarding state.
So in rapid spanning tree there are two types of blocked ports.
An alternate port is a port that is blocked because it's receiving more useful BPD use from another
bridge on the segment.
So in this example, this port is the designated port on let's say switch B on, switch A, this port
is an alternate port because more useful or better BPAs are being received on this segment from Switch
B, then from switch A, and that may be because the priority of switch B is lower than the priority
of Switch A.
A backup port is a port that is blocked because it's receiving more useful BPD use from the same bridge
that it's on.
So in this example, we're assuming that this port, this port and this port are connected to a hub.
This port becomes the backup port.
It's connected to the same switch as this designated port, but it may be a higher port number.
Therefore, it becomes the backup port.