How to get a list of all valid IP addresses in a local network?

Install nmap,

sudo apt-get install nmap

then

nmap -sP 192.168.1.*

or more commonly

nmap -sn 192.168.1.0/24

will scan the entire .1 to .254 range

This does a simple ping scan in the entire subnet to see which hosts are online.

Try following steps:

1. Type ipconfig (or ifconfig on Linux) at command prompt. This will give you the IP address of your own machine. For example, your machine's IP address is 192.168.1.6. So your broadcast IP address is 192.168.1.255.
2. Ping your broadcast IP address ping 192.168.1.255 (may require -b on Linux)
3. Now type arp -a. You will get the list of all IP addresses on your segment.

If you want to see which IP addresses are in use on a specific subnet then there are several different IP Address managers.

Try Angry IP Scanner or Solarwinds or Advanced IP Scanner