What is spanning tree protocol and why is it important?

One of the biggest issues that network administrators face when designing a switched network is the prevention of loop. In network topology changes always happen and if in case a loop forms then the traffic that passes through the affected switches can easily drain out the entire bandwidth allocated to these switches. There are several solutions to handle such issue but the best way to prevent the formation of loops in a switched network is to deploy the Spanning Tree Protocol (STP).

What is Spanning Tree Protocol?

STP is a standardized solution provided by IEEE which helps to prevent loop formation in data networks. It was invented by Dr. Radia Perlman.

In a switched network all the switches generate data messages, which are known as Bridge Protocol Data Units (BPDUs). The working principle behind the exchange of BPDUs is that switches will be able to indentify redundant paths in a network by applying the STP algorithm and ensure that no loops are formed. The STP algorithm identifies all active redundant links and blocks them to prevent the formation of loops. The entire working of Spanning Tree Protocol can be broken down into three easy steps

Step 1: All STP enabled switches in a network elect a root bridge. All the switches exchange messages (BPDUs) among themselves and elect a root bridge. This process is known as Root Bridge Election.

Step 2: The second step is known as Root Port Election. Once all switches have elected a Root Bridge, the next part is to decide which port of a switch will communicate with the Root Bridge.

Step 3:  The final step is to have only one active path left open in every part of the network and bypass the creation of a loop. This is known as Designated Port Election.

What is Spanning Tree Protocol Important?

STP’s importance lies in the fact that it provides data redundancy to all devices in a network. It means the every connection has a backup so that it is able to send data in case the primary connection is down. However, only one path is open at a time. In the event that the open path experiences any error another path will open up ensuring constant flow to data to all devices. STP also prevents the formation of bridge loops so that the entire bandwidth allocated doesn’t get drained. Loops occur when there are multiple open paths for data transmission which can result for errors in data processing and forwarding. With STP only one path is open at a time thus eliminating loops.

Topology changes happen all the time in any network and more so in large networks. But network failure even for a few seconds can bring about serious consequences especially for multinational organizations. Spanning tree protocol ensures that the network keeps running without any data loss between devices and makes high availability of a network possible. Conventional STP takes around 50 seconds to adapt to any changes in the network but for large networks this is a lot of inactivity time. Currently a new upgraded version of STP is available called Rapid Reconfiguration or Fast Spanning Tree which cuts down on convergence time and helps recover quickly from network failure or session timeouts.