CCNA 新版（英文）D20S03L03.pps

© 2002, Cisco Systems, Inc. All rights reserved.
© 2002, Cisco Systems, Inc. All rights reserved.
2
Spanning-Tree Protocol Overview
Objectives
pleting this lesson, you will be able to:
Describe the purpose and operation of the STP
Explain how to implement STP to solve the problems associated with redundant switched or bridged topologies
Provides a loop-free work topology by placing certain ports in the blocking state.
Spanning-Tree Protocol
One root bridge work
One root port per nonroot bridge
One designated port per segment
Nondesignated ports are unused
Spanning-Tree Operation
Bpdu = Bridge Protocol Data Unit  (default = sent every two seconds)
Root bridge = Bridge with the lowest bridge ID
Bridge ID =
In the example, which switch has the lowest bridge ID?
Spanning-Tree Protocol Root Bridge Selection
Spanning-tree transits each port through several different states:
Spanning-Tree Port States
Spanning-Tree Port States (Cont.)
Spanning-Tree Path Cost
Spanning-Tree Example