Comment by cetra3

UDP and TCP are Layer 3 protocols, and so is ICMP. They all fill the same bits within network packets, like at the same level. So sending an ICMP packet (protocol 1) is not the same as sending a UDP packet (protocol 17).

You can see a list of network protocols in /etc/protocols actually, or here: https://www.iana.org/assignments/protocol-numbers/protocol-n...