STP – Spanning Tree Protocol.
Active protocol by default
Routing protocols deal with Level 3 network redundancy.
The Spanning-Tree handles the level 2 network redundancy.
Goal of the Spanning Tree:
Get a loopless architecture.
But what if I have loops on my network?
In a world without Spanning Tree
Let's take this architecture as an example.
This network is a full-mesh network (all our active equipment is connected to each other).
The Spanning-tree protocol has been disabled.
A customer sends a broadcast on the network.
The switch to which it is connected will broadcast this broadcast on all its ports except on the port where it received it.
This step repeats itself …
And will be repeated indefinitely!!!
Our equipment will be overloaded and our network will become unusable.
A network without spanning-tree is necessarily a star network!
If a network loop is created (intentionally or by accident) our network will be out of service.
Without Spanning-Tree, we have three problems:
Broadcast Storm (Broadcast Storms)
Broadcasts on our network will take almost all of our bandwidth.
Instability of MAC tables
A broadcast is created when a host does not know the recipient's MAC address. All the equipment that will see this frame pass will be said "I received a message from AAAA:BBBB:CCCC on port 0/1, so this host is on port 0/1, I will note this information in my MAC table". Two seconds later, he receives this same frame on the 0/2 port, so he will update his MAC table indefinitely without ever knowing where this host is actually…
Multiple distribution of our frames
As we have seen before, all broadcasts will circulate indefinitely between active equipment for nothing.
By default, the spanning-tree is activated on every CISCO switch. Which avoids all these problems.
In a world with Spanning Tree
The spanning-tree protocol will logically create a loopless architecture. (Star in this case)
If a link falls, the logical architecture will be updated.
Types of Spanning Tree
The Spanning–Tree Protocol (STP) is a standardized IEEE protocol.
It uses Trunk links to work.
The IEEE Institute and CISCO have a different approach to STP. So they each have their own versions.
The Rapid-STP protocol (RSTP) is the improved version of the STP.
You can see in the table below these versions of the Spanning-Tree as well as their differences.
Before you understand how all these versions of the Spanning-tree works, it's important to understand how the STP protocol works!
So I give you an appointment in the article "STP Protocol"!!
Hoping this article has been helpful to you! Don't hesitate to let me know!!