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I know ICMP uses IP datagrams to reply to echo requests but what is above that?

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  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin ♦
    Commented Aug 15, 2017 at 5:06
  • As the other answers say, there is no higher protocol or level above ICMP. I recommend you to install Wireshark on your PC and capture some packets. You will learn a lot by just observing your own traffic.
    – Michael Alvarez
    Commented Oct 20, 2018 at 20:55

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ICMP is actually part of IP. There is no protocol above IP that responds to an ICMP Echo Request. ICMP itself, as part of IP, responds with the ICMP Echo Reply. From RFC 792 INTERNET CONTROL MESSAGE PROTOCOL:

ICMP, uses the basic support of IP as if it were a higher level protocol, however, ICMP is actually an integral part of IP, and must be implemented by every IP module.

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ICMP is a protocol itself. See INTERNET CONTROL MESSAGE PROTOCOL. There is no higher level protocol required. For example, in Cisco IOS, some ICMP access lists look like:

access-list 102 permit icmp any any echo-reply
access-list 100 permit icmp 192.168.1.0 0.0.0.255 any echo
access-list 100 permit icmp any 192.168.1.0 0.0.0.255 echo-reply
access-list 100 deny icmp 192.168.1.0 0.0.0.255 192.168.2.0 0.0.0.255 time-exceeded

Notice port numbers are not specified because there are none.

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