Spanning Tree Protocol

KEY POINT

STP is a Layer 2 protocol that prevents logical loops in switched networks that have redundant links.

The following sections examine why such a protocol is needed in Layer 2 networks. STP terminology and operation are then introduced.

Redundancy in Layer 2 Switched Networks

Redundancy in a network, such as that shown in Figure 1-18, is desirable so that communication can still take place if a link or device fails. For example, if switch X in this figure stopped functioning, devices A and B could still communicate through switch Y. However, in a switched network, redundancy can cause problems.

Figure 1-18 Redundancy in a Switched Network Can Cause Problems a

- 0260.60AA.AAAA

Switch X

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