[jzm2k]

Is there any P2P network that fits that criteria? The first time you connect, you need to know at least one publicly reachable node but I fail to see how that relates to WebSocket/WebRTC. I think central server is somewhat ambiguous because the bootnode could be any node on the network you have prior knowledge of.

[lostmsu]

As I mentioned in the sibling, there's multicast/broadcast (classic multiplayer games used it) and you could do IP scanning.

[jzm2k]

I still don't understand what this has to do with WebRTC/WebSocket. You can combine, e.g., mDNS with WebRTC and build a pure peer-to-peer network.