designated bridge for the sample shown in Figure
If BRIDGE_3 is told that it is not the designated bridge, it will go into blocking state. In blocking state the bridge monitors the network but is not involved in forwarding packets. BRIDGE_3 then would only become the designated bridge with a change in the network, for example, if the designated bridge fails or another bridge is added to the network that would change the root path cost for BRIDGE_3.
Spanning Tree Example
Figure B-2 shows a Spanning Tree configuration with multiple Bridge Modules.
B - 4 ONline Ethernet Bridge Module Installation and Operation Guide