How to find all the used IP addresses on a network

Generally, nmap is quite useful to quickly scan networks.

To install nmap, enter the following command in the terminal:

sudo apt-get install nmap

Once the application is installed, enter the following command:

nmap -sn 192.168.1.0/24

This will show you which hosts responded to ping requests on the network between 192.168.1.0 and 192.168.1.255.

For older versions of Nmap, use -sP:

nmap -sP 192.168.1.0/24

For additional references, see the following pages:

NMAP Installation Guide

NMAP Reference Guide

It is a very useful tool to learn.

If all the computers in your network are Ubuntu or any other distribution that makes use of avahi-daemon (DNS-SD), you can get a detailed list of them (with hostname and IP address) by doing:

avahi-browse -rt _workstation._tcp

If you want to know all the IP addresses used in your network, you can use arp-scan:

sudo arp-scan 192.168.1.0/24

As it is not installed by default, you'll have to install it with sudo apt-get install arp-scan. arp-scan send ARP packets to the local network and displays the responses received, so it shows even firewalled hosts (that block traffic based on IP packets).