External and local IP addresses both serve the same purpose, the difference is scope. An external or public IP address is used across the entire Internet to locate computer systems and devices. A local or internal IP address is used inside a private network to locate the computers and devices connected to it.
External (Public) IP Address
Your Internet Service Provider (ISP) assigns you an external IP address when you connect to the Internet. When your web browser requests a webpage, it sends this IP address along with it. Your ISP uses this to know which of its customers are requesting which webpage. Also, any website that you visit will have access to this IP address.
Your external IP address is:
Every website also has an IP address of its own, though you never need to know them. When you type in the domain name, such as "www.google.com", a Domain Name Server (DNS) looks up the IP address for you, which is the real location of the website. In this way, domain names are like human-friendly names pointing to machine-friendly IP addresses.
Local (Internal) IP Address
If your computer is connected to a router with default settings, that router will automatically assign a local IP address to your computer. Your local IP address is hidden from the outside world and used only inside your private network. You generally don't need to know much about it unless you're trying to set up a game or web server.
The local IP address can change depending on what other devices are connected to the same network and in what order they were connected. Most network routers assign IP addresses starting at 192.168.1.2, and increment the last digit with each new device that connects.
For example: If you turn on your computer first and it is the only device connected to your network, it will probably be assigned the local IP address 192.168.1.2. Then if you turn on your laptop and connect to the network it will probably be assigned the local IP address 192.168.1.3. And so on and so forth (the IP address 192.168.1.1 is generally reserved for the router itself).
You can assign devices specific IP addresses in the router control panel, so that a device will always receive the same local IP address when it connects. This is called a static local IP address. Consult your router manual for more information.
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