Hey guys,

I was wondering how Games like Terraria's new multiplayer works, as in before that big update last year, a multiplayer server required portforwarding but now people can just invite there friends to play a game and it requires no portforwarding what so ever.

So what I am wondering is why doesn't it require portforwarding and how does that way work, as I assume they are using some sort of tech valve has, like steamworks?

Cheers

Edit:
https://partner.steamgames.com/documentation/api

So I was looking around, is it peer to peer

Almost certainly they implemented NAT punchthrough and/or UPNP.

See the Forum FAQ entry #9 for links to reading material.

If it's a Steam game and you're using the Steam SDK it's all done for you. Steam does the tunneling and packet reflection for you. It uses libjingle for nat-punch-through, and dedicated relay servers.

Cheers