3com 9100 User Manual

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STP Configurations
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Figure 17   Tag-based STP configuration
The tag-based network i
 has the following configuration:
Switch 1 contains VLAN Marketing and VLAN Sales.
Switch 2 contains VLAN Engineering and VLAN Sales.
Switch 3 contains VLAN Marketing, VLAN Engineering, and VLAN 
Sales.
The tagged trunk connections for three switches form a triangular 
loop that is not permitted in an STP topology.
All VLANs in each switch are members of the same STPD.
STP may block traffic between Switch 1 and Switch 3 by disabling the 
trunk ports for that connection on each switch.
Switch 2 has no ports assigned to VLAN marketing. Therefore, if the 
trunk for VLAN marketing on Switches 1 and 3 is blocked, the traffic for 
VLAN marketing will not be able to traverse the switches.
Marketing & Sales
Marketing, Sales & Engineering
Sales & Engineering
Switch 1
Switch 3
Switch 2
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