mDNS traffic is very easy to pick and filter. probably you're thinking dht, but even then, you can block the primed node list or just ask any other client which ip are on the network and block those.
this is not the average sysad we're talking, it's a state actor with access to all local isps resources.
Yes, DHT, mdns (for local nets), and manual connections via `ipfs swarm connect`. You can get a peers address through any other open means of communication, connect to them, and then through them, get other peers information. All it takes is one good node
