We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What is the Spanning Tree Protocol?

By Rodney A. Crater
Updated May 16, 2024
Our promise to you
EasyTechJunkie is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At EasyTechJunkie, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject-matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

Network devices that act as open systems interconnection (OSI) model layer two bridging devices, including switches, are often connected together redundantly to help prevent network failures. The spanning tree protocol (STP) is a set of rules, methods and communications functions that are implemented in bridge software and that prevent data link layer frames from endlessly looping within a redundant bridge topology. The spanning tree protocol is a data link layer protocol that establishes a singular, lowest-cost pathway for data to travel from any one bridged network endpoint to another.

Bridges that use the spanning tree protocol send special messages called bridge protocol data units (BPDUs) to each other in order to share information and notify each other about network changes. Most bridges participate in the spanning tree process, but network administrators might designate some bridges as pass-through-only devices. All of the bridging devices that actively use the spanning tree protocol exchange BPDUs in order to establish and maintain a loop-free, minimum spanning tree topology.

STP initiates recalculation of a new spanning tree topology whenever bridges are added to or removed from the network, when pathways fail within the network, when undirectional link detection (UDLD) detects a broken fiber or when other topological changes occur and disrupt the established flow of data. The bridges that actively use the spanning tree protocol begin topological reconfiguration by first agreeing upon and designating one of the bridging devices as a root node for the new spanning tree. They then collaborate by sending BPDUs to each other that contain current information and path costs in order to calculate a new spanning tree that has the lowest cost for the topology. As soon as the bridges agree on a new topology, bridge ports connected to redundant segments that are not a part of the new spanning tree and are not part of a designated etherchannel are temporarily blocked to prevent forwarding of data traffic. Blocking these unused redundant pathways creates a loop-free topology.

The spanning tree protocol was first developed and implemented by the Digital Equipment Corporation (DEC). It was shortly thereafter incorporated into the Institute of Electrical and Electronics Engineers(IEEE) 802.1D standard. A newer, faster version of the spanning tree protocol called the rapid spanning tree protocol (RSTP) was introduced by the IEEE 802.1w proposal. RSTP has superseded STP as the standard protocol for loop-free bridging and was designated as the protocol of choice in the revised IEEE 802.1D-2004 standard. STP has been refined even further with the release of the multiple spanning tree protocol (MSTP) as detailed in IEEE 802.1Q-2005, which allows separate instances of STP to coexist in multiple virtual local area network (VLAN) configurations.

EasyTechJunkie is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
EasyTechJunkie, in your inbox

Our latest articles, guides, and more, delivered daily.

EasyTechJunkie, in your inbox

Our latest articles, guides, and more, delivered daily.