How to find the WAN IP Address?

Your local network is behind a router which is connected to your Internet Provider. All traffic coming to your computer is via your router which then routes the traffic to your local IP Address.

One way to find your WAN IP address, the address assigned to you by your Internet Provider is go to the site.

http://getmywanip.com/

Which immediately responds by showing your WAN IP Address as well as your host server as shown for my ISP Provider:

WANIPFinder.png

What is STUN and why do I need a STUN Server?

Skype is quite well known. You can call up someone using your web browser to speak to him if he is also on the Internet or even his cell phone if he has a Skype UserId / Password or Skype account. This is made possible by VOIP (voice over Internet) using the VoIP protocol.

Now what is STUN?

STUN is Session Traversal of User Datagram Protocol (UDP) through Network Address Translators(NAT).

If you are using the IP Phone from behind the firewall (where NAT becomes important) then STUN allows you setup Phone calls to aVoIP Provider hosted outside your local network (typical example is a home network consisting of computers connected to a router).

While your voice calls go through the router to the STUN Server, the STUN server can connect to your local machine behind the firewall.

STUNServer_00
Read more here. The above image was from this link.

What is NAT?

NAT is Network Address Translation. A network device such as a firewall or router assigns public address to one or more computers inside a private network.

In Home computers, for example, if you have a number of connected (wired/wireless) computers then each of them can have a public address. These computers can share resources like files/folders inside the private network. A router is involved in routing the traffic between them.

Here is an example of 3 computers (wi-fi) forming the internal network with the router as the default gateway.

NAT conserves the number of public addresses. In the example you would have required 3 public addresses to connect to Internet.