Acing the CCNA Exam, Volume 1

15 Rapid Spanning Tree Protocol

This chapter covers

• The standard and Cisco-proprietary versions of Spanning Tree Protocol
• A comparison of the port costs, states, and roles of STP and Rapid STP
• How RSTP-enabled switches react to topology changes
• How RSTP link types affect convergence
• Optional STP features Root Guard, Loop Guard, and BPDU Filter

In this chapter, we will continue to look at Spanning Tree Protocol (STP). There’s a reason STP is enabled by default on almost any vendor’s switches: Layer 2 loops are disastrous for a LAN. However, there are some downsides to the original STP as defined by IEEE 802.1D, the main one being speed; it can take up to 50 seconds to converge and reach a new, stable state after a change in the LAN. When STP ...