问题
Is there a difference in the meaning of external IP address vs public IP address and internal IP address vs private IP address?
回答1:
Yes, external and public IP address would be the same thing, and internal or private IP adress is the one you have inside your firewall/router. So for example, if you have a BT homehub, it will give your machine an IP address like 192.168.1.65. The external IP address is what your router uses to send/receive data OUTSIDE of the firewall that is part of the router. You can see what your IP address is by going to a website like this one: http://whatismyipaddress.com/ (It's usually also possible to figure out deep down in some menu in the administration of your router, but all routers are pretty much different user interfaces, so it's hard to explain where/how)
There are two reasons for using internal IP addresses:
There is a shortage of "free" ip addresses, so if everyone's computer had a public IP address, we'd be playing musical chairs, but with far less chairs than people... By having private IP addresses, many computers can use the same private IP address, with just a few routers connected to the actual public network with a public IP address.
There is a certain element of increased security by not allowing a direct route to every machine inside the firewall, so by having machines with private IP addresses inside the firewall - to an attacker, the inside of the firewall is just a big black box.
You can find out your own ip address by checking the settings on your network card. In Windows, ipconfig will show the network cards and their IP addresses. On a linux system ifconfig will show the same type of information.
来源：https://stackoverflow.com/questions/14026981/are-the-terms-external-ip-address-and-public-ip-address-synonomous