Personally, I couldn’t care less about Terraria, although it reminds me a bit of Zelda III back in the day, but it does have this multiplayer capability. But it never mentions the TCP port. Well the default port is:
And if you have an Apple airport network, a teenager that needs to have ‘cut off times’ and sits 2 levels of NAT in, you’ll have to forward TCP 7777 all the way to their computer. It’s not the end of the world but UPNP doesn’t work in nat-nat scenarios (thankfully) but the blasted game doesn’t mention when setting up a network game, oh by the way you’ll need to NAT TCP 7777.
Oh well that is all.