Though some research has been done on reliable UDP multicasting, I haven't yet used anything like that.  You should take into consideration that this might not be as trivial as it first sounds.

If you don't have a list of nodes in the target network you have no idea when and to whom to resend, even if active nodes receiving your messages can acknowledge them.  Sending to a large number of nodes, expecting acks from all of them might also cause congestion problems in the network.

I'd suggest to rethink the network architecture of your application, e.g. using some kind of centralized solution, where you submit updates to a server, and it sends this message to all connected clients.  Or, if the original sender node's address is known a priori, then just let clients connect to it, and let the sender push updates via these connections.

Reliable udp broadcast libraries?
Is there a way to use a standard Matrix Keypad to set a synchronous counter IC without having to use a micro controller?
