You can ping a device to see ifs its reachable. Gave a basic answer due to the nature of this interview. He answered the other 2 which the question involves CEH...... I remember him stating that you can tell by what operating system it is. Didn't want to say but hopefully he is reading this: TTL (Time-To-Live) value clues: Sometimes you can infer the OS from the TTL in a ping reply: Windows default TTL: 128 Linux/Unix default TTL: 64 (((((But note: this can be spoofed or changed and is not reliable alone.)))))