External VS Internal IP Addresses

In simpler terms:-
An external address is like a telephone number that anyone can phone.
It has to be unique (and should be allocated to you).
(Imagine if two people had the same phone number for completely different houses - who would get the call - similar problem would occur with computers with the same external number).
Using that IP address (telephone number) any other computer connected to the web can talk to you (any phone on the phone exchange can phone you), unless you limit them in some way (firewalls etc - a bit like call barring).

An internal address is more like an extension number within an office.

It is unique within that office but another office belonging to another company may have the same internal extension number. It does not have to be allocated by an external authority - it is controlled by the company itself. Depending on how things are set-up, external computers may be able to talk to your computer or may not - similar to an internal phone.

some of the internal IP address are:

10.0.0.0/8 (commonly used)
127.0.0.0/8 (loopback addresses)
169.254.0.0/16 (Micro$haft range)
172.16.0.0/16 (least commonly used)
192.168.0.0/24 (most commonly used)

These are USUALLY non routable because internet routers are configured to not route them. You can route them on your own network if you setup the network hardware to route them over you WAN or through your VPN tunnel.

An external/public/WAN IP is what is used out on the big bad internet.Internal IPs are sometimes referred to as virtual IPs. They are a group of up to 255 IPs that are used and recognized internally on the local area network. They are not intended to be recognized on the Internet.Real Ip as is external ip, The real IP from ISP, instead, can be recognized or pinged by another real IP. The Prestige 310 Internet Access Sharing Router works like an intelligent router that routes between the virtual IP and the real IP.

for finding your external IP address
goto command prompt and type  IPCONFIG

then it will show you your external IP address
EX: IPv4 Address : 101.210.65.23
and if you are connected to a LAN(Local Area Network),then you can find your internal IP address in the

 " Network And Sharing Center -->Local Area Network-->properties-->Internet Protocol Version 4(TCP/IPv4)

Hope this will be usefull for you...