In this question, August Vrubel has some C code that sets up a tun interface and then injects a packet, but the packet seemed to disappear into the ether. In this post, I’d like to take a slightly extended look at my answer because I think it’s a great opportunity for learning a bit more about performing network diagnostics. The original code looked like this: c original sendpacket.c #include <arpa/inet.h> #include <fcntl.