Chapter 2. Bridging and LAN Switching

Spanning Tree Protocol


802.1D Spanning Tree Protocol (STP) is a Layer 2 loop-prevention mechanism. It is an IEEE standards-based protocol. Over the years, Cisco enhanced this protocol with new features to make much-needed improvements. This chapter discusses those improvements and new IEEE versions of the protocol that dramatically improve the technology. Layer 2 loops are terrible because of no Time To Live (TTL) value in frames. Loops can cause broadcast storms, MAC table corruption, and multiple-frame copies.

STP Process

The bridge ID (BID) is a critical element for the creation of the spanning-tree, loop-free topology. The bridge ID consists of a 2-byte bridge priority and a 6-byte MAC address. ...

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