A private IP address is an IP address that's reserved for internal use behind a router or other Network Address Translation (NAT) device, apart from the public. Private IP addresses are in contrast to public IP addresses, which are public and can't be used within a home or business network. Sometimes a private IP address is also referred to as a local IP address.Jie En Lee / Ach5
Which IP Addresses Are Private?
The Internet Assigned Numbers Authority (IANA) reserves the following IP address blocks for use as private IP addresses:10.0.0.0 to 10.255.255.255172.16.0.0 to 172.31.255.255192.168.0.0 to 192.168.255.255
The first set of IP addresses allow for over 16 million addresses, the second for over 1 million, and over 65,000 for the last range.
Another range of private IP addresses is 169.254.0.0 to 169.254.255.255, but those are for Automatic Private IP Addressing (APIPA) use only.
In 2012, the IANA allocated 4 million addresses of 100.64.0.0/10 for use in carrier-grade NAT environments.
Why Private IP Addresses Are Used
Instead of having devices inside a home or business network each use a public IP address, of which there's a limited supply, private IP addresses provide an entirely separate set of addresses that allow access on a network but without taking up a public IP address space.
For example, most routers in homes and businesses across the globe have the IP address of 192.168.1.1, and assign 192.168.1.2, 192.168.1.3, ... to the various devices that connect to it (using DHCP).
It doesn't matter how many routers use the 192.168.1.1 address, or how many dozens or hundreds of devices inside that network share IP addresses with users of other networks because they aren't communicating with each other directly. Instead, the devices in a network use the router to translate requests through the public IP address, which can communicate with other public IP addresses and eventually to other local networks.
The hardware within a specific network that's using a private IP address can communicate with all the other hardware within the confines of that network but require a router to communicate with devices outside the network, after which the public IP address is used for the communication.
For example, before landing on this page, your device (such as a computer, phone, or tablet), which uses a private IP address, requested this page through a router, which has a public IP address. Once the request was made and Ach5 responded to deliver the page, it was downloaded to your device through a public IP address before reaching your router, after which it was handed off to your private/local address to reach your device.
All the devices (laptops, desktops, phones, tablets, and others) that are contained within private networks around the world can use a private IP address with virtually no limitation, which can't be said for public IP addresses.
Private IP addresses also provide a way for devices that don't need a connection to the internet, such as file servers and printers, to communicate with the other devices on a network without being directly exposed to the public.
Reserved IP Addresses
Another set of IP addresses that are restricted even further are called reserved IP addresses. These are similar to private IP addresses in the sense that they can't be used to communicate on the internet, but they're even more restrictive than that.
The most famous reserved IP is 127.0.0.1. This address is called the loopback address and is used to test the network adapter or integrated chip. No traffic addressed to 127.0.0.1 is sent over the local network or public internet.
Technically, the entire range from 127.0.0.0 to 127.255.255.255 is reserved for loopback purposes but you'll almost never see anything but 127.0.0.1 used in the real world.
Addresses in the range from 0.0.0.0 to 0.255.255.255 are also reserved but don't do anything at all. If you're even able to assign a device an IP address in this range, it will not function properly no matter where on the network it's installed.
How to Find Your Private IP Address
Knowing your private IP address is only helpful in specific, and for most people rare, situations.
If you want to connect one computer to another on your network, for example, a mapped network drive, you can do so through its local IP address. You can also use a local IP address with remote desktop software to control a computer from afar. A private IP address is also needed to direct a specific network port from a router to a particular computer on the same network, a process called port forwarding.
The easiest way to find your private IP address in Windows is to use Command Prompt with the ipconfig command.
Not sure what your router or other default gateway's private IP address is? See How Do I Find My Default Gateway IP Address?.
More Information on Private IP Addresses
When a device such as a router is plugged in, it receives a public IP address from an ISP. It's the devices that connect to the router that are given private IP addresses.
Private IP addresses can't communicate directly with a public IP address. This means if a device that has a private IP address is connected directly to the internet, and therefore becomes non-routable, the device will have no network connection until the address is translated into a working address through a NAT, or until the requests it sends are sent through a device that does have a valid public IP address.
All traffic from the internet can interact with a router. This is true for everything from regular HTTP traffic to FTP and RDP. However, because private IP addresses are hidden behind a router, the router must know which IP address it should forward information to if you want an FTP server to be set up on a home network. For this to work properly for private IP addresses, port forwarding must be set up.
Forwarding one or more ports to a specific private IP address involves logging into the router to access its settings, and then choosing which ports to forward and to where they should go.