Digital Router Question:

ICMP is the Internet Control Message Protocol. Most users will recognize the name through the use of tools such as ping and traceroute, as this is the protocol that these services run over among other things. Its primary purpose is to tell systems when they are trying to connect remotely if the other end is available. Like TCP and UDP, it is a part of the IP suite and uses IP port number 1. Please note, this is not TCP port 1 or UDP port 1 as this is a different numbering scheme that for reference can be located here (For your reference, TCP uses IP port 6, while UDP uses IP port 17). That being said, different functions of ICMP use specific ports on TCP and UDP. For example, the 'echo' portion of ping (the part where someone else is able to ping you) uses TCP port 7.