We will use nmap. If you don’t have access to a machine with it, just use the test from the service below: http://nmap.online-domain-tools.com/ The parameters to be used are: -T5 -sS -p 1-65535 your.ip.address (If you are using the online tool above, check “Custom Scan”, enter the parametes above and click “Scan Now”) If you have access to a machine with nmap (outside your network - for example, a digital ocean droplet), just run it with the same parameters above. How to interpret the results:

• Any ports that are listed as closed can be used.
• Any ports listed as filtered are firewalled.
• Whether they’re firewalled by your router or higher up at your ISP is something you’ll have to figure out by tinkering with your router.

Output examples:

FROM A MACHINE WITH NMAP:

nmap -T5 -sS -p 1-65535 201.68.217.170

Starting Nmap 6.40 ( http://nmap.org ) at 2014-10-05 16:45 EDT Nmap scan report for 201-68-217-170.dsl.telesp.net.br (201.68.217.170) Host is up (0.56s latency). All 65535 scanned ports on 201-68-217-170.dsl.telesp.net.br (201.68.217.170) are filtered Nmap done: 1 IP address (1 host up) scanned in 322.30 seconds

FROM THE SERVICE “nmap.online”:

Starting Nmap 6.45 ( http://nmap.org ) at 2014-10-05 22:03 Central Europe Daylight Time Nmap scan report for 201-68-217-170.dsl.telesp.net.br (201.68.217.170) Host is up (0.27s latency). Not shown: 65534 filtered ports PORT STATE SERVICE 51005/tcp open unknown Nmap done: 1 IP address (1 host up) scanned in 309.11 seconds