Nortel BayStack 410 24T Using Manual page 71

To connect multiple VLANs across switches with redundant links, the STP must
be disabled on all participating switch ports.
consequences of enabling the STP when using VLANs between untagged
(non-802.1Q tagged) switches.
Communications
Figure 1-23.
As shown in
S2 is forwarding at any time. Communications failure occurs between VLAN 2 of
S1 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 forwarding
link based on port speed, duplex mode, and port priority. Because the other link
connecting VLAN 2 is placed into Blocking mode, stations on VLAN 2 in switch
S1 cannot communicate with stations in VLAN 2 on switch S2. With multiple
links only one link will be forwarding.
309985-B Rev 00
Station A
No
Station B
Possible Problems with VLANs and Spanning Tree Protocol
Figure 1-23, with STP enabled, only one connection between S1 and
Introduction to the BayStack 410-24T Switch
Figure 1-23
VLAN 1
Forwarding
VLAN 1
shows possible
Non-802.1Q
tagged switch
S1
VLAN 2
Blocking
Non-802.1Q
tagged switch
S2
VLAN 2
BS41022A
1-43