FORE Systems ES-2810 Ethernet Switch User’s Manual
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Concepts in Switching
Concepts in Switching
A.7.2 Spanning Tree Protocol
A.7.2.1 Spanning Tree Protocol Concept
Since alternative paths are desirable for backup and other purposes, IEEE and ISO have pro-
posed a standard to solve the problem of “network loops”. The solution is called “The Span-
ning Tree Protocol”, and is described in IEEE document 802.1D, “Local MAC Bridges”.
A.7.2.2 Bridging Loops
Within the Spanning Tree Algorithm, switches connected in a LAN must detect potential
“bridge loops”, and then remove these loops by blocking the appropriate ports to other
switches. This is illustrated in the following diagram:
Figure A.2 -
Spanning Tree and Bridge Loops
An alternate path has been established by connecting Switch B in parallel with Switches A and
C — this also creates a potential bridge loop. However, by using the Spanning Tree Algorithm,
Switch B breaks the loop and blocks its path to segment 3.
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