STP Configurations 93Figure 17 Tag-based STP configurationThe tag-based network in Figure 17 has the following configuration:n Switch 1 contains VLAN Marketing and VLAN Sales.n Switch 2 contains VLAN Engineering and VLAN Sales.n Switch 3 contains VLAN Marketing, VLAN Engineering, and VLANSales.n The tagged trunk connections for three switches form a triangularloop that is not permitted in an STP topology.n All VLANs in each switch are members of the same STPD.STP may block traffic between Switch 1 and Switch 3 by disabling thetrunk ports for that connection on each switch.Switch 2 has no ports assigned to VLAN marketing. Therefore, if thetrunk for VLAN marketing on Switches 1 and 3 is blocked, the traffic forVLAN marketing will not be able to traverse the switches.Marketing & Sales Marketing, Sales & EngineeringSales & EngineeringSwitch 1 Switch 3Switch 291_010
