Uses of Spanning Trees

Spanning Tree defuses loops.

The primary function of Spanning Tree Protocol is to ensure redundancies that appear in your network don’t turn into loops that cause larger problems over time. By locating potential connections in switches, that if unchecked would repeat infinitely until the network’s memory crashed, Spanning Tree allows optimization and elimination of unnecessary faults in data forwarding.

How Spanning Tree Works

Spanning Tree eliminates loops between switches by first identifying a situation where the conduit would go eternally. It then goes in and blocks one of the links in the looping system until the active problem because unusable, and forces future usage to flow through another available path. The method Spanning Tree uses to determine which linkage it will block is entirely dependent on what parts of the network’s topology it can read.

Eliminating Loops

Once the culprit switches in the loop in the system have been identified, Spanning Tree looks for another subset of the same topology free of loops. It measures this subset to make sure it has connectivity to the entire network, across the entire LAN. These bridges will perform the Spanning Tree procedure upon original connection, and each time the topology of the system is altered, therefore continuing to keep the system in check and free of errors as the network grows over time.

Configuration Method

Break loops before they happen.

Because the Spanning Tree Protocol runs each time the system is updated, it waits to be alerted by a configuration message that will set it off. When it begins, a root bridge is identified in the network, which is the basis around which the topology is defined. Each bridge thereafter will look for the shortest path to the root bridge so it can locate the center of the system. Each LAN then elects the bridge closest to this root, and each individual bridge selects a port through which it will send data to the root. Every bridge port in Spanning Tree works in this manner unless it is marked “Ignore.”

Spanning Tree Usage

Because this method of system evaluation happens every time the network topology changes, there will be brief system pauses (around 50 seconds) during which traffic is held up for the Spanning Tree calculation. This causes a short downtime while the potential switch failure is reconfigured, though obviously the downtime is much shorter than if the switch were allowed to explode. As well, newer versions of the Spanning Tree algorithm have been designed to operate faster, narrowing the downtime with each innovation.

References

• Enterprise Networking: Networking 101
• Cisco: Understanding Spanning Tree