What happens if I try to send an UDP packet larger than the maximum packet size of the medium - say a 3000 bytes packet (as the title suggests, I use the SDL_Net library)?

The packet will be fragmented and then later reassembled by the receiving stack. This can be done either by the sender (if the MTU for its network is smaller than the packet size) or by a router along the way (if it has a segment with a smaller MTU).

Thanks.