He has a quick summary of the different types of spending tree and the advantages and disadvantages
of each.
So the original version of Spending Tree is the triple E, a 2.1 D spanning tree.
This is the legacy standard of spending tree that was used when bridges were around.
So it's very old, but it's the basis of other versions of Spending Tree.
You'll also see the term C is DT or common spanning tree.
This assumes that there is one spanning tree instance for the entire bridged network, regardless of
the number of VLANs.
We don't use that today in Cisco environments.
We use a version of per VLAN, spanning tree or PVS.
DT Originally PvZ.
DT Only supported ESL PvZ.
DT Plus supports ESL and ADA 2.1.
Q But today we often refer to PVS plus as PVS DT.
So this is a Cisco enhancement of spending tree that provides a separate ed to one DX spanning tree
instance for every VLAN.
If you had 100 VLANs, you would end up having 100 instances of spanning tree.
Each spanning tree would have its own route and would do its own calculations in Cisco environments.
Each spanning tree would send its own BPD use or bridge protocol data units.
So if you had 100 VLANs every 2 seconds, a hundred BPD user sent multiple spanning tree tries to optimize
PVS DT by mapping multiple VLANs to the same spanning tree instance.
So 82.1 SW or multiple spanning tree allows you, for example, to have two spanning tree instances
and then split your VLANs.
Between those instances, VLANs 1 to 100 could be associated with instance one.
VLANs 101 to 200 could be associated with instance two.
That provides a lot of advantages in that you have two instances of spanning tree rather than 200,
which you would have if you used PVS.
DT Multiple spanning tree also has rapid spanning tree built into it, so it converges very quickly.
Rapid spanning tree or ADA 2 to 1 W improves convergence over the 1998 version of Spanning Tree by adding
roles to ports and enhancing BPU exchanges.
It provides for much quicker convergence when compared to traditional spending tree.
Rapid spending tree.
However, only supports a single instance of spending tree.
So all the lands are mapped to that single instance.
And this is why we have a rapid pivot plus on Cisco switches that allows us to have one spanning tree
instance per VLAN but have rapid convergence.
Now multiple spanning tree has the advantage that you can map multiple VLANs to a single instance of
spanning tree.
That, however, only becomes important when you have many VLANs.
If, for example, you only have ten VLANs in your enterprise.
Rapid pivot plus works really well and hence it's the default spanning tree on Cisco switches.
You would only necessarily need to use multiple spanning tree if you had hundreds or thousands of VLANs.
So the default today on most Cisco switches is rapid PvP plus provides rapid convergence and allows
you to configure one spanning tree instance per VLAN to optimize performance in the videos.
In this course, I'll show you a campus network where we optimize spanning tree by splitting the load
between different switches.
In other words, one switch will be the spanning tree route for some VLANs and another switch will be
the spanning tree route for other VLANs.