Figure B-1. Spanning Tree Network Architecture
When a bridge is installed into a network, it assumes that it is the root of the network until it is told otherwise. We will call this bridge BRIDGE_3. Thinking it is root, BRIDGE_3 transmits packets onto all the networks to which it is connected, letting adjacent bridges know that it believes it is root. If an adjacent bridge sees that there is a bridge more deserving of the title root bridge of the Spanning Tree (i.e., having a lower “bridge address”), that bridge will inform BRIDGE_3 and it will no longer claim to be root.
BRIDGE_3 has another chance to enter the hierarchy by becoming one of the designated bridges. Each LAN has a designated bridge whose role is to transfer information between that LAN and the root. BRIDGE_3 asks all the adjacent bridges, except those on its root port, whether it can become the designated bridge for any of those neighbor's LANs. If BRIDGE_3 is closer to the root than any of the neighboring bridges on a particular LAN, then it will become the designated bridge for that LAN. BRIDGE_3 is the
