Not all machines are pingable

To check if a machine(IP) is reachable, I only used ping. If ping is not working, then I will come to a conclusion that IP is not reachable. If you are like me, please read further.

How Ping works?

Ping sends the ICMP Echo to the given IP and waits for the ICMP Echo Reply. If we get the Echo Reply, then ICMP server in the given IP is able to send response to our Echo request. We can have timeouts for this roundtrip.

So if we didn’t get Echo Reply can we assume that given IP is not reachable. No, it is not true.

Reasons for ping not working:

1) ping command has been disabled for that network (by the syadmin)
2) You have no Internet connection/network connectivity
3) A firewall can filter ICMP Echo messages
4) IP is not actually reachable

Then, how to test the reachability of an IP

1) If you know the port,
    1) `telnet IP PORT` once connected, we cannot disconnect
    2) `curl IP:PORT` (hope, get call shouldn't be a problem)
2) If you don't know the port,
    1) `traceroute IP`

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