Descubrir los hosts de una red con nmap

La utilidad nmap se asocia a un escaner de puertos, pero también podemos usarlo para descubrir hosts que respondan a ping sin realizar ningún escaneado de puertos.
Mediante la opción -sn podemos deshabilitar el escaneado de puertos para usar únicamente el host discovery:

-sn: Ping Scan - disable port scan

A continuación únicamente deberemos indicar la red a descubrir para obtener todos los host que respondan a ping:

$ sudo nmap -sn 10.1.9.0/24

Starting Nmap 5.50 ( http://nmap.org ) at 2011-08-18 19:55 CEST
Nmap scan report for 10.1.9.0
Host is up (0.0092s latency).
Nmap scan report for 10.1.9.1
Host is up (0.024s latency).
Nmap scan report for 10.12.9.3
Host is up (0.024s latency).
Nmap scan report for 10.1.9.4
Host is up (0.024s latency).
Nmap scan report for 10.1.9.5
Host is up (0.024s latency).
Nmap scan report for 10.1.9.6
Host is up (0.024s latency).
Nmap scan report for 10.12.9.7
Host is up (0.024s latency).
Nmap scan report for 10.1.9.11
Host is up (0.0097s latency).
Nmap scan report for 10.1.90.13
Host is up (0.014s latency).
Nmap scan report for 10.1.9.14
Host is up (0.013s latency).
Nmap scan report for 10.1.9.254
Host is up (0.0064s latency).
Nmap done: 256 IP addresses (11 hosts up) scanned in 1.76 seconds 

Fuente:http://systemadmin.es/2011/08/descubrir-los-hosts-de-una-red-con-nmap