How to do it...

To make an ICMP echo request, open your terminal and enter the following command:

# nmap -sP -PE scanme.nmap.org

If the host responded, you should see something similar to this:

# nmap -sP -PE scanme.nmap.org 


Nmap scan report for scanme.nmap.org (74.207.244.221) 
Host is up (0.089s latency). 
Nmap done: 1 IP address (1 host up) scanned in 13.25 seconds 

How it works...

The arguments -sP -PE scanme.nmap.org tell Nmap to send an ICMP echo request packet to the host scanme.nmap.org. We can determine that a host is online if we receive an ICMP echo reply to this probe.

SENT (0.0775s) ICMP 192.168.1.102 > 74.207.244.221 Echo request (type=8/code=0) ttl=56 id=58419 iplen=28 
RCVD (0.1671s) ICMP 74.207.244.221 > 192.168.1.102 Echo reply (type=0/code=0) ttl=53 id=24879 iplen=28 
Nmap scan report for scanme.nmap.org (74.207.244.221) 
Host is up (0.090s latency). 
Nmap done: 1 IP address (1 host up) scanned in 0.23 seconds 

There's more...

Unfortunately, ICMP has been around for a pretty long time, and remote ICMP packets are now usually blocked by system administrators. However, it is still a useful ping technique for monitoring local networks.

$ nmap -sP -PP <target>
$ nmap -sP -PM <target>

See also