Using sockets to Send()/Receive() After that, the information of the network (L4/L3/L2) set by the OS was only organized abstractly, but when I saw the actual code logic (especially the logic that directly creates and interprets packets) and data being sent/received without sockets, it felt like I had been hit in the head with a hammer. I think I have also gained a deeper understanding of the network. Wow, thank you!