Spanning Tree Protocol | Spanning Tree States

Fig 1: Spanning Tree Protocol | Spanning Tree States

Spanning Tree Protocol is the layer 2 protocol which is used to avoid the loops of the layer 2 basically it is a loop avoidance protocol and the algorithm of the STP is Spanning Tree Algorithm and this algorithm was invented by the "Radia Perlman". This protocol provide us the logically loop free topology for the network of ethernet. The standard of Spanning tree protocol is IEEE 802.1D.

Spanning Tree Protocol Terms

Root Bridge
Designated Port
Root Port
Non Root Bridge

Spanning Tree Algorithm

Spanning Tree Protocol algorithm is STA that work is avoid the loops in the ethernet network on the basis of the calculations of the spanning tree protocol terms in different locations of the network. Spanning tree algorithm calculate terms like:

Root Bridge Per Network
Designated Port Per Segment
Root Port Per Non Root Bridge

Root Bridge/Network

The first major thing that is calculated by the algorithm is root bridge and root bridge is selected on the basis of the election and election is occur on the basis of the following terms:

Switch Priority

If any switch in the network has lowest switch priority will win the election and will be a Root Bridge and the default value of switch priority is 32768 and it is configurable parameter.

MAC Address

If the switch priority of the switches in the network is same then the election will be done on the base of the MAC address and If any switch in the network has the lowest Mac address in term of hexadecimals than that switch will be a Root Bridge and the MAC address never same because it is a unique address.

Designated Port/Segment

Designated Port is the port of the switch that is the best BPDU (Bridge Protocol Data Unit) transmitter. BPDU packet consist of the following parameters:

Root Bridge ID
Cost to the Root
Sender Bridge ID
Sender Port ID

Root Port/Non Root Bridge

Root Port is the port of the switch that is the best BPDU receiver and these ports are elected on the non root bridge.

Final Conclusion

After the working on the selection of the terms the remaining port or ports goes in the temporarily blocking state and the signal of the blocking port is the color of orange in below figure so that way the loops of the layer 2 avoid in the ethernet network.

Fig 2:Spanning Tree Protocol Active

Spanning Tree States

Following are the five states of the spanning tree protocol which are known as spanning tree states:

Disable State
Blocking State
Listening State
Learning State
Forwarding State

So there is approximately 50 seconds required from disable state to the forwarding state and from blocking state to forwarding state we required 30 seconds. In enterprise network it is very time taking process to come in the forwarding state. It is very time consuming process.