How can I install an IP scanner for Ubuntu 16.04 LTS?

Here are two that work reasonably well with Ubuntu 16.04 LTS.

The first one, arp-scan, accomplished the primary goal of ennumerating devices. The second one, nmap, is much more versatile and gives a quick picture of the services available from each device.

1) arp-scan

Installation is easy:

sudo apt-get update
sudo apt-get install arp-scan

It has a ton of options, which can be seen here:

sudo arp-scan --help

For basic enumeration, to scan my "local" net, is:

sudo arp-scan -l | sort

Which results in a very basic display which shows each device including IP address, MAC address and manufacturer of the interface. It also showed "dup" responses for some of the addresses.

2) nmap

sudo apt-get update
sudo apt-get install nmap

To run a Fast scan, which lists devices and shows open ports

nmap -F 192.168.8.1-254

The result is a fairly complete list of devices and open ports.

Here is a handy NMAP Cheat Sheet to see some of the ways to use nmap.

I am surprised neither is installed by default in Ubuntu 16.04, but it is quick and easy to make both of them work.