3Com 3800 User Manual page 105

STP Configurations 7-7
When the Switches in this configuration start up, STP configures each
STP domain 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 7-4, 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 any STPD,
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.