A Quick Introduction about Spanning Tree Protocol

The Spanning Tree Protocol, also known as Spanning Tree, is the Waze or MapQuest of contemporary Ethernet networks, guiding traffic along the most effective path depending on real-time conditions.

Based on an algorithm developed by American computer scientist Radia Perlman while she was employed by Digital Equipment Corporation (DEC) in 1985, the primary objective of Spanning Tree is to eliminate redundant links and communication pathway looping in complicated network setups. As a supplementary function, Spanning Tree can route packets around difficulty regions to ensure that communications can traverse networks experiencing disturbances.

Spanning Tree V/S Ring Topology

In the 1980s, when corporations were just beginning to network their computers, the ring network was one of the most common designs. 1985 saw the introduction of IBM’s proprietary Token Ring technology.

Each node in a ring network topology is connected to two additional nodes, one located ahead of it on the ring and one located behind it. Signals move around the ring in a single direction, with each node passing on any packets that are looping around the ring.

When hundreds or thousands of devices are added to a network, simple ring networks become inefficient. Ring networks are effective when there are only a handful of computers. In order to communicate information with a single machine in an adjacent room, a computer may need to send packets through hundreds of nodes. Bandwidth and throughput become problematic when traffic can only go in one direction and there is no backup plan in the event that a node along the route becomes damaged or unduly busy.

Spanning Tree won the LAN topology battles in the 1990s when Ethernet became faster (100Mbit/sec Fast Ethernet was released in 1995) and the cost of an Ethernet network (bridges, switches, and cabling) became much less than Token Ring.

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How Spanning Tree Protocol Works?

Spanning Tree is a data packet forwarding protocol. It is equal parts traffic cop and civil engineer for the network roadways on which data moves. It resides at Layer 2 (data link layer), therefore it is only concerned with transferring packets to their proper destination, regardless of the type of packets or the data they carry.

Spanning Tree has become so prevalent that its use is outlined in the IEEE 802.1D standard for networking. According to the specification, there can be only one active path between any two endpoints or stations for them to function effectively.

Spanning Tree is meant to prevent data travelling across network parts from becoming caught in a loop. Loops typically confound the forwarding algorithm built in network devices, causing the device to no longer know where to transmit packets. This may cause frames to be duplicated or duplicate packets to be forwarded to various destinations. It is possible for messages to be repeated. Communications might return to the sender. It can even bring a network to its knees if too many loops occur, using bandwidth without providing any noticeable benefits and obstructing other non-looped traffic.

The Spanning Tree Protocol prevents loop formation by limiting each data packet to a single potential path. Switches on a network utilise Spanning Tree to construct root pathways and bridges over which data can travel, and to cut off duplicate paths, leaving them inactive and unusable while a primary path is accessible.

Consequently, network communications flow seamlessly, regardless of how complex or extensive a network may become. In a sense, Spanning Tree provides single channels for data to go through a network using software, much like network engineers did with hardware in the days of loop networks.

Benefits of Spanning Tree Protocol

Spanning Tree is employed primarily to avoid the potential of routing loops within a network. But there are additional benefits as well.

Because Spanning Tree is continually searching for and defining which network paths are accessible for data packets to traverse, it can detect if a node along one of these key paths has been deactivated. This can occur for a variety of reasons, including a hardware breakdown or a change in network setup. It may be a temporary condition dependent on bandwidth or other variables.

When Spanning Tree recognises that a major path is no longer active, it might swiftly open a previously closed secondary path. It can then transfer data around the problem, eventually designating the detour as the new principal way or sending packets back to the original bridge if it becomes available again.

While the original Spanning Tree made new connections very quickly, the IEEE released the Rapid Spanning Tree Protocol in 2001. (RSTP). RSTP, also known as the 802.1w version of the protocol, was created to offer substantially faster recovery in the event of network changes, temporary outages, or component failure.

While RSTP added additional path convergence behaviours and bridge port roles to speed up the process, it was supposed to be fully compatible with the original Spanning Tree. Therefore, it is conceivable for devices supporting both versions of the protocol to coexist on the same network.

Drawbacks of Spanning Tree Protocol

In spite of the fact that Spanning Tree has become commonplace in the many years since its inception, there are those who feel that its time has come. The greatest flaw of Spanning Tree is that it blocks off potential data paths inside a network, hence closing off potential loops. In any network utilising Spanning Tree, around forty percent of available data pathways are closed.

In very complex networking systems, such as those found in data centres, the capacity to scale up fast to meet demand is essential. Without the restrictions imposed by Spanning Tree, data centres may open up significantly more bandwidth without requiring new networking infrastructure. This is a somewhat amusing circumstance, given that Spanning Tree was designed for complex network situations. And now, the protocol’s protection against looping is, in a sense, preventing these ecosystems from reaching their full potential.

Multiple-Instance Spanning Tree (MSTP) was designed to deploy virtual LANs and let multiple network paths to be open simultaneously while preventing loop formation. However, even with MSTP, a significant number of potential data pathways remain closed on networks adopting the protocol.

There have been numerous non-standardized, separate attempts throughout the years to improve the bandwidth limitations of Spanning Tree. While the inventors of some have claimed success, the most majority are not fully compatible with the core protocol, necessitating that companies either implement the non-standard changes on all of their devices or find a method for them to coexist with switches running conventional Spanning Tree. In most instances, maintaining and supporting several Spanning Tree variants is not worth the expense.