Making Sure Special Command Arrived

[Strikerklm96]

In my game, when the Host hits "Launch", it sends data in a udp packet to each of the clients to let them know what level to load, and what entity they are in control of. How can I make sure they received it? Could I just send it several times? Is this where I would want to use TCP? Will packets ever be completely lost, or just delayed/out of order?

[Jesper Juhl]

Yes. This is where you want TCP or you can use a library like ENet that builds a reliable channel on top of UDP.
Plain UDP does not provide guaranteed delivery and there is no way to determine if what you sent is recieved or lost. And yes, packets get lost completely and you will not be told about it. They also sometimes arrive out-of-order and more. The internet is a hostile network environment.

[eXpl0it3r]

There is no guarantee of delivery, ordering, or duplicate protection.

Might want to read up on the topics you're working with.

Adding a reliable protocol on top of UDP (like Enet does) is only a good choice in very few cases.
If you want reliability, use TCP.