Block non-local connections on mdns server

[gmaclennan]

We create a tcp server for listening to mdns connections, but theoretically this could receive connections from outside the local network.
We should reject/block incoming connections from non-local addresses. We can maybe do this by checking socket.remoteAddress against private IP ranges with something like https://github.com/mafintosh/bogon
The reason for doing this is a security precaution, particularly if we are sending invites to peers discovered through mdns, and we want to be sure that incoming connections are local network only.

[tomasciccola]

I was wondering how can we test this. Should we have a publicly accessible node that does mdns and connects to a predefined topic, so we can reject it on a test? Or is there already a mdns testnet that we can use?

[gmaclennan]

This should be fixed in the latest implementation