nmap:tldr:acc38

The command "nmap -sn ${ip_or_hostname} ${optional_another_address}" is used to perform a host discovery scan using the nmap network exploration tool.

Here is a breakdown of the command:

• "nmap": This is the command used to invoke the nmap tool.
• "-sn": This is an option in nmap that stands for "No port scan." It tells nmap to skip the port scanning phase and only perform host discovery.
• "${ip_or_hostname}": This is a placeholder for the IP address or hostname of the target system you want to scan. Replace it with the actual IP address or hostname you want to scan.
• "${optional_another_address}": This is an optional argument that allows you to specify additional IP addresses or hostnames to scan. You can list multiple addresses or hostnames separated by spaces.

When you run this command, nmap will use ICMP (Internet Control Message Protocol) echo requests by default to discover hosts and determine if they are active or not. It will send an ICMP echo request to the specified IP address or hostname(s) and listen for responses. If a response is received, nmap considers the host to be active.

This command is useful to quickly identify active hosts on a network without performing a full port scan, which can take longer. However, keep in mind that some hosts may be configured to block ICMP echo requests, which could result in false negatives.