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C H A P T E R 9 Spanning Tree Protocol (STP)
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• 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 9.1: Multiple Spanning Tree Domains - VLAN tagging
for trunk connections
When the switches in this configuration start, STP configures each
STPD such that there are no active loops in the topology. STP can
configure the topology in several ways to make it loop-free.
In Figure 9.1, 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 was not 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 Switches A and B, and between Switches Y and Z.
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
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