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CCNP Quick Reference Sheets Bundle: Exams 642-901, 642-812, 642-845, 642-825 by Jay Swan, Denise Donohue, Brent Stewart

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Chapter 3. Spanning Tree

Ethernet network design balances two separate imperatives. First, Ethernet has no capacity for detecting circular paths. If such paths exist, traffic loops around and accumulates until new traffic is shut out (this is called a broadcast storm). Second, having secondary paths is good preparation for inevitable link failure.

Spanning Tree is a protocol that prevents loop formation by detecting redundant links and disabling them until needed. Designers can therefore build redundant links and the protocol will allow one to pass traffic and keep the other in reserve. When the active link fails, the secondary link is enabled quickly.

Understanding the Spanning Tree Protocol

Switches either forward or filter Layer 2 frames. The ...

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