Siju GeorgeICMP (Internet Control Message Protocol) is the most helpful network protocol to help diagnose and troubleshoot connectivity problems.
Suppose you cannot access the Internet on your desktop PC. What will you do?
The first thing you will do is to ping the Google from the Command Prompt.
Why do you ping a domain name or IP address?
The ping will give you the error code related to the connectivity problem that blocks the Internet from your computer.
ICMP generates those error codes.
One of the Popular ICMP replies is the Destination Host Unreachable.
So, what does this ICMP error reply mean?
The Destination Host Unreachable error means the remote device you ping from your computer is unavailable.
The remote device might be down, or your computer does not know the route to the device.
See how helpful this error reply is.
Another critical ICMP error reply is Destination Net Unreachable.
If the ping packets from your laptop fail to find the route to the destination network, ICMP will send a Destination Net Unreachable message.
The first ICMP reply tells the destination host is unavailable. The second ICMP reply tells us the destination network is unavailable.
So, you learned the importance of ICMP replies in network connectivity troubleshooting.
Request Timed Out:
It is one of the ICMP replies while ping in the middle of a network connectivity problem. This error message tells your computer waited but has received any ICMP reply for the ping packets sent.
Let me explain it with an example. You cannot access the Internet from your Windows laptop. So, you ping the Google from the Command Prompt.
The ping reply shows the Request Timed Out instead of a packet received message.
It means your computer waited for the ICMP replies from the Google server. But your computer has not received any response.