So here’s a quick comparison of the different versions of Spanning Tree.
The Spanning Tree 802.1D protocol doesn’t need a lot of resources
but it slow to converge.
You only have 1 Spanning Tree instance for your entire layer 2 network.
This can lead to sub-optimal traffic flows
and 802.1D is generally not used today in Cisco environments.
Just be aware that when you use newer versions of Spanning Tree
Cisco switches are backward compatible
and can talk to all the switches or non-Cisco switches using 802.1D
PVST is the Cisco enhancement
that provides a single instance of Spanning Tree per-VLAN.
It's Cisco propriety, it needs more resources
because 1 Spanning Tree instance is created per-VLAN.
It is still slow to converge but thus allow you to split traffic flows
because you have 1 Spanning Tree instance per VLAN.
as an example, VLAN 1 traffic could use 1 uplink
but VLAN 2 traffic could use as separate uplink or a separate port in a network.
Cisco have also enhanced PVST with features
such as Portfast, Uplink fast, backbone fast, BPDU guard, BPDU filter
root guard and loop guard we'll discuss some of those terms in this course
otherwise, you'll learn more about those when you attend your CCMP courses.
Rapid Spanning Tree Protocol or 802.1W is an industry standard protocol
it doesn’t need as many resources as PVST+
because it supports a single instance of Spanning Tree for your layer 2 network.
Its big advantage is that it provides very quick or fast convergence.
It also doesn’t address suboptimal traffic flow issues
because you can send VLAN 10 traffic for example down 1 link
and VLAN 20 traffic down another link.
That’s the advantage of Rapid PVST+
Rapid PVST+ incorporates the advantages of Rapid Spanning Tree
but allows you to create 1 spanning tree instance per-VLAN
so you can do load sharing of traffic, it provides very quick convergence
but uses a lot of resources especially when you’ve got many VLANs.
The advantage of Multiple Spanning Trees
is that it solves that high resource issue of PVST+
Multiple Spanning Trees allows you to create an instance of Spanning Tree
and then map various VLANs to that instance.
As an example, once again if you had 200 VLANs PVST or Rapid PVST
would require 200 instances of Spanning Tree
where’s Multiple Spanning Tree could use 2 instances to do load sharing
and reduce the amount of resources required.
So CPU and memory requirements for Multiple Spanning Trees
are lower than those for Rapid PVST+
but resources are higher than those for Rapid Spanning Tree.
Now you may find reference materials stating that PVST+
is the default Spanning Tree on Cisco switches
that really depends on a lot of switches today use Rapid PVST
is the default version of Spanning Tree.