* Listar puertos abiertos:

  nmap -sT -O localhost

* Mirar puerto abierto UDP:
# nmap -p <puerto> -sU -P0 <ip>

Ejemplo:
  #  nmap -p 5060 -sU -P0 10.139.56.4

  Starting Nmap 5.00 ( http://nmap.org ) at 2013-01-19 20:32 UTC
  Interesting ports on 10.139.56.4:
  PORT     STATE         SERVICE
  5060/udp open|filtered sip



* Manual para ver conexiones rechazadas:

http://www.linuxjournal.com/article/6447

* Host discovery:

  nmap -sn 192.168.1.0/24

<code>
Starting Nmap 6.00 ( http://nmap.org ) at 2012-09-06 05:59 EDT
Nmap scan report for 192.168.1.1
Host is up (0.028s latency).
Nmap scan report for 192.168.1.199
Host is up (0.00031s latency).
Nmap done: 256 IP addresses (2 hosts up) scanned in 4.48 seconds
</code>