Chapter . Spanning Tree

Protecting the Flat Earth of Networking

The Spanning Tree Protocol (STP) is a Layer 2 protocol designed to run on bridges and switches. The main purpose of spanning tree is to prevent loops from forming in a bridged network. The de-facto implementation of STP is based on the Institute of Electrical and Electronic Engineers (IEEE) 802.1d standard.

Loops form when redundant connections between switches form a circular path; the same packet travels endlessly around the same path in a circle. Multicast and broadcast packets are the culprits for bringing down networks when loops form because the packet is not destined to a single device, and no device is responsible for removing the packet from the network.

Loops can be deadly, ...

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