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Unity Multiplayer Networking pitfalls

So recently I need to find a way to get two Unity projects on different machines talking and sharing data. The data shared is nothing like multiplayer games, far from it, it was just a notification of an event flag that became true on one machine. So if a special event happens on one machine then the other machine will also know. This is just sending a string or an int as a flag, simple!

My first attempt was to use Unity's Unet Multiplayer Networking system. It looks easy enough to use right ? So I followed the Networking tutorial here. Turns out it was not as smooth as I'd hoped...

  • The server only works as standalone. So we need to build the application and run as standalone. Not a big problem, but for those who don't read the manuals (like me, hehe) this is the first obstacle. Just running on the Editor will not work.
  • However, it does not work between computers. I was running a mac and a windows machine and although they could see each other just fine (ping worked) the Unity projects could not talk to each other.
  • After many hours googling, I tried everything I found, disabling firewall, antivirus, tutorials, sample codes etc. It just didn't work.
During my search I saw many people posting the same thing, basically it doesn't work between different devices on a local network. I guess there must be something I did wrong somewhere but the documentations and tutorials do not cover multiple devices on LAN.

So the next thing I tried was to use the transport layer (LLAPI) as discussed in this post. I got it to work on the same PC, but not over the network. It turns out that in order to get it to work you need to connect the two devices to each other. In other words,  if you have devices on 192.168.2.10 and 192.168.2.12 you need to have 
connectionId = NetworkTransport.Connect(socketId, "192.168.2.10", remoteDevicePort, 0, out error);

on the machine with the IP 192.168.2.12 and conversely,
connectionId = NetworkTransport.Connect(socketId, "192.168.2.12", 4999, 0, out error);

on the machine with the IP 192.168.2.10.
Oh, and last but not least, the two devices need to run the same version of Unity. If the versions don't match, the connection may fail silently.

With the above setup, I managed to get two PCs on LAN to send messages back and forth as P2P.

Hope this post helps.

PS : The repository of this test project.

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