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Configuring Catalyst Switch Operations

Configuring Catalyst Switch Operations. Introducing Spanning Tree Protocol. Outline. Overview Spanning Tree Protocol Spanning-Tree Operation Root Bridge Selection Spanning-Tree Port States Spanning-Tree Path Costs Spanning-Tree Recalculation Rapid Spanning Tree Protocol Summary.

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Configuring Catalyst Switch Operations

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  1. Configuring Catalyst Switch Operations Introducing Spanning Tree Protocol

  2. Outline • Overview • Spanning Tree Protocol • Spanning-Tree Operation • Root Bridge Selection • Spanning-Tree Port States • Spanning-Tree Path Costs • Spanning-Tree Recalculation • Rapid Spanning Tree Protocol • Summary

  3. Spanning Tree Protocol • Provides a loop-free redundant network topology by placing certain ports in the blocking state

  4. Spanning-Tree Operation • One root bridge per broadcast domain • One root port per nonroot bridge • One designated port per segment • Nondesignated ports are unused

  5. Spanning Tree Protocol Root Bridge Selection • BPDU (default = sent every two seconds) • Root bridge = bridge with the lowest bridge ID • Bridge ID = • In this example, which switch has the lowest bridge ID?

  6. Spanning-Tree Port States • Spanning tree transits each port through several different states:

  7. Spanning-Tree Port States (Cont.)

  8. Spanning-Tree Operation

  9. Spanning-Tree Path Cost

  10. Spanning-Tree Recalculation

  11. Spanning-Tree Convergence • Convergence occurs when all the switch and bridge ports have transitioned to either the forwarding or the blocking state. • When the network topology changes, switches and bridges must recompute STP, which disrupts user traffic.

  12. Rapid Spanning-Tree Protocol

  13. Rapid Transition to Forwarding

  14. Summary • STP is a bridge-to-bridge protocol used to maintain a loop-free network. • To maintain a loop-free network topology, STP establishes a root bridge, a root port, and designated ports. • With STP, the root bridge has the lowest BID, which is made up of the bridge priority and the MAC address. • When STP is enabled, every bridge in the network goes through the blocking state and the transitory states of listening and learning at power up. If properly configured, the ports then stabilize to the forwarding or blocking state. • If the network topology changes, STP maintains connectivity by transitioning some blocked ports to the forwarding state. • RSTP significantly speeds the recalculation of the spanning tree when the network topology changes.

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