Any Broadcast message can be transmitted as a Multicast message, thereby limiting searches, chats, etc to nodes that have subscribed to it. Each node is identified by a unique guid plus a hash of his ip address creating a 20 byte address. Replies are routed quicker, and methods can be put in place to optimize the routing. Only upstream and peer nodes get duplicates in broadcast scenarios. Nodes do not generate traffic from every other node on the network when connecting.
Packets travel primarily upstream to nodes that have elected to receive greater traffic.
Nodes should be able to flag when data has changed. Since broadcasts aren't routed down if the originating node lives downstream, client B can spoof as client A, causing none of client A's broadcasts to reach people on the leg of the network the client B is on. The ip addresses should be hashed in clientid. Broadcast and multi-cast floods could possibly affect the entire network. All top tier nodes must be connected directly or indirectly to each other via their peer network.