Introduction to the BayStack 410-24T Switch309985-B Rev 00 1-43To connect multiple VLANs across switches with redundant links, the STP mustbe disabled on all participating switch ports. Figure 1-23 shows possibleconsequences of enabling the STP when using VLANs between untagged(non-802.1Q tagged) switches.Figure 1-23. Possible Problems with VLANs and Spanning Tree ProtocolAs shown in Figure 1-23, with STP enabled, only one connection between S1 andS2 is forwarding at any time. Communications failure occurs between VLAN 2 ofS1 and VLAN 2 of S2, blocking communications between Stations A and B.The link connecting VLAN 1 on Switches S1 and S2 is selected as the forwardinglink based on port speed, duplex mode, and port priority. Because the other linkconnecting VLAN 2 is placed into Blocking mode, stations on VLAN 2 in switchS1 cannot communicate with stations in VLAN 2 on switch S2. With multiplelinks only one link will be forwarding.S2S1VLAN 1 VLAN 2VLAN 1 VLAN 2BlockingStation ANoCommunicationsStation BForwardingNon-802.1Qtagged switchBS41022ANon-802.1Qtagged switch
