DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
Understanding and Troubleshooting the Spanning Tree Protocol 337
This is a common network design. The switches C and D have
redundant links to the backbone switches A and B using
trunks. Trunks, by default, carry all the VLAN traffic from
VLAN 1 and VLAN 2. So switch C is not only receiving traffic
for VLAN 1, but it is also receiving unnecessary broadcast and
multicast traffic for VLAN 2. It is also blocking one port for
VLAN 2. Thus, there are three redundant paths between