FORE Systems ES-2810 Ethernet Switch User’s Manual
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Concepts in Switching
Concepts in Switching
A.9.2 Warning When Using VLANs
It is important to be aware of problems that may arise when using Spanning Tree and VLANs.
The Spanning Tree can use alternative paths (such as different ports) to get messages to their
destination. VLANs specify which ports can receive messages.
Figure A.6 -
Spanning Tree and VLANs
In the above diagram, we have two switches. To the left, we see the two switches connected
and the ports are grouped in two VLANs: A and B. On the right, we have enabled STP; STP
blocks the path between X and Z (to avoid looping) and, therefore, destroys the VLAN setup
(because the VLAN needs these ports to receive messages).
Switch 2
Switch 1
B
B
A
A
WX
Y
Z
VLAN STP
VLAN
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