UNIX for Dummies Questions & Answers

Yes, UDP, TCP, and ICMP must travel inside an IP datagram. There are lots of other protocols as well. You can get a list of which protocols your system supports by looking at /etc/protocols. The IP header has an 8 bit field called protocol which is how the IP layer tells them apart.

But you can stash an illegal value in the protocol field, one which corresponds to no known protocol. You can't call it anything but just IP. People often use "packets" to refer to the union of datagrams and packets. So it makes sense to say TCP, UDP, ICMP, and IP packets. The last one is just acting as a catch-all.

AoE, look into hping2, it's a pretty straightforward tool, and it's all done from the command line as options.