Nortel 1000BASE-LX, Using Manual, Page: 61 / 214

Chapter 2 Network configuration 61
Using the BayStack 420 10/100/1000 Switch
Because there is only one link between the two switches, the Spanning Tree
Protocol (STP) treats this configuration as any other switch-to-switch connection.
For this configuration to work properly, both switches must support the 802.1Q
tagging protocol.
VLANS spanning multiple untagged switches
Figure 18 shows VLANs spanning multiple untagged switches. In this
configuration, Switch S2 does not support 802.1Q tagging and you must use a
single switch port on each switch for each VLAN.
For this configuration to work properly, you must set spanning tree participation
to Disabled (the STP is not supported across multiple LANs).
Figure 18 VLANs spanning multiple untagged switches
When the STP is enabled on these switches, only one link between each pair of
switches will be forwarding traffic. Because each port belongs to only one VLAN
at a time, connectivity on the other VLAN is lost. Exercise care when configuring
the switches to ensure that the VLAN configuration does not conflict with
spanning tree configuration.
VLAN 1
S1
S2
VLAN 2
BayStack 420
Untagged ports
Non-802.1Q
tagging switch
10005EA