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STP Configurations
Summit 300-48 Switch Software User Guide 147
• Marketing is defined on all switches (switch A, switch B, switch Y, switch Z, and switch M).
Two STPDs are defined:
• STPD1 contains VLANs Sales and Personnel.
• STPD2 contains VLANs Manufacturing and Engineering.
The VLAN Marketing is a member of the default STPD, but not assigned to either STPD1 or STPD2.
Figure 15: Multiple Spanning Tree Domains
When the switches in this configuration start up, STP configures each STPD such that there are no
active loops in the topology. STP could configure the topology in a number of ways to make it loop-free.
In Figure 15, the connection between switch A and switch B is put into blocking state, and the
connection between switch Y and switch Z is put into blocking state. After STP converges, all the
VLANs can communicate, and all bridging loops are prevented.
The VLAN Marketing, which has not been assigned to either STPD1 or STPD2, communicates using all
five switches. The topology has no loops, because STP has already blocked the port connection between
switch A and switch B, and between switch Y and switch Z.
Within a single STPD, you must be extra careful when configuring your VLANs. Figure 16 illustrates a
network that has been incorrectly set up using a single STPD so that the STP configuration disables the
ability of the switches to forward VLAN traffic.
LB48014
Sales, Personnel, Marketing
STPD 1
STPD 2
Manufacturing, Engineering, Marketing
Sales, Personnel, Manufacturing, Engineering, Marketing
Switch A Switch Y
Switch Z
Switch M
Switch B