How the Spanning Tree Protocol Works
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How the Spanning
Tree Protocol Works
Using the Spanning Tree Protocol (STP), bridges transmit messages to
each other that allow them to calculate the Spanning Tree topology.
These messages are special packets called
Configuration Bridge Protocol
Data Units
(CBPDUs), or configuration messages.
CBPDUs at Work
CBPDUs do not propagate through the bridge as regular data packets do.
Instead, each bridge acts as an end station, receiving and interpreting
CBPDUs.
Bridge Hierarchy
The CBPDUs help bridges establish a hierarchy (or a
calling order
) among
themselves for the purposes of creating a loopless network.
Based on the information in the CBPDUs, the bridges elect a
root bridge
,
which is at the top level of the hierarchy. The bridges then choose the
best path on which to transmit information to the root bridge.
The bridges that are chosen as the best path, called
designated bridges
,
form the second level of the hierarchy:
■
A designated bridge relays network transmissions to the root bridge
through its
root port
. Any port that transmits to the root bridge is a
root port.
■
The designated bridges also have
designated ports
— the ports that
are attached to the LANs from which the bridge is receiving
information.
Figure 20 shows the hierarchy of the STP bridges and their ports.
Summary of Contents for CoreBuilder 3500
Page 44: ...44 CHAPTER 2 MANAGEMENT ACCESS ...
Page 58: ...58 CHAPTER 3 SYSTEM PARAMETERS ...
Page 86: ...86 CHAPTER 5 ETHERNET ...
Page 112: ...112 CHAPTER 6 FIBER DISTRIBUTED DATA INTERFACE FDDI ...
Page 208: ...208 CHAPTER 9 VIRTUAL LANS ...
Page 256: ...256 CHAPTER 10 PACKET FILTERING ...
Page 330: ...330 CHAPTER 12 VIRTUAL ROUTER REDUNDANCY PROTOCOL VRRP ...
Page 356: ...356 CHAPTER 13 IP MULTICAST ROUTING ...
Page 418: ...418 CHAPTER 14 OPEN SHORTEST PATH FIRST OSPF ...
Page 519: ...RSVP 519 Figure 94 Sample RSVP Configuration Source station End stations Routers ...
Page 566: ...566 CHAPTER 18 DEVICE MONITORING ...
Page 572: ...572 APPENDIX A TECHNICAL SUPPORT ...
Page 592: ...592 INDEX ...