Exam 100-101 Topic 4 Question 9 Discussion

ping may be used to find out whether the local machines are connected to the network or whether a remote site is reachable. This tool is a common network tool for determining the network connectivity which uses ICMP protocol instead of TCP/IP and UDP/IP. This protocol is usually associated with the network management tools which provide network information to network administrators, such as ping and traceroute (the later also uses the UDP/IP protocol). ICMP is quite different from the TCP/IP and UDP/IP protocols. No source and destination ports are included in its packets. Therefore, usual packet-filtering rules for TCP/IP and UDP/IP are not
applicable. Fortunately, a special "signature" known as the packet's Message type is included for
denoting the purposes of the ICMP packet. Most commonly used message types are namely, 0, 3,
4, 5, 8, 11, and 12 which represent echo reply, destination unreachable, source quench, redirect,
echo request, time exceeded, and parameter problem respectively.
In the ping service, after receiving the ICMP "echo request" packet from the source location, the
destination