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CCNP Routing and Switching Quick Reference Library: ROUTE 300-101, SWITCH 300-115, and TSHOOT 300-135 Quick References by Brent Stewart, Denise Donohue

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Chapter 4. Spanning Tree Protocol

Ethernet network design balances two separate imperatives. First, having multiple ways to reach a destination is generally a good thing. Redundant links proactively prepare the network for inevitable link failure. Second, Ethernet has no way to detect circular paths. If such paths exist, traffic loops around until it is stopped by some external force (such as a network admin pulling out a cable) because there is no Time-to-Live field in an Ethernet header.

Spanning Tree Protocol (STP) prevents loop formation by detecting redundant links and disabling them until needed. Designers can therefore build networks with redundant connections, and the protocol enables one link to pass traffic while keeping the other in ...

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