User’s Guide FUJITSU PSWITCH
December/2018 69
stations in VLAN 20 have a single path to communicate with other VLAN 20
devices.
The following Figure 3-5 shows the logical single STP network topology.
Figure 3-5: Single STP Topology
For VLAN 10 this single STP topology is fine and presents no limitations or
inefficiencies. On the other hand, VLAN 20's traffic pattern is inefficient. All frames
from Switch B will have to traverse a path through Switch A before arriving at
Switch C. If the Port 2 on Switch B and Switch C could be used, these inefficiencies
could be eliminated. MSTP does just that, by allowing the configuration of MSTIs
based upon a VLAN or groups of VLANs. In this simple case, VLAN 10 could be
associated with Multiple Spanning Tree Instance (MSTI)1 with an active topology
similar to Figure 3-5 and VLAN 20 could be associated with MSTI 2 where Port 1 on
both Switch A and Switch B begin discarding and all others forwarding. This simple
modification creates an active topology with a better distribution of network traffic
and an increase in available bandwidth.
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