When you look at the network settings on a smartphone or PC, an IP address may be displayed.
However, that IP address is not necessarily the same one that websites can see.
In home and workplace networks, devices are often assigned IP addresses for the inside network. Then, when they communicate with the internet, the router uses a mechanism called NAT to map inside communication to outside communication.
This article organizes the point that "the IP address displayed on the device" and "the IP address visible to a website" may be different.
IP addresses have a visible scope
An IP address is not necessarily visible in the same way from everywhere.
The IP address displayed on a smartphone or PC inside a home is used on the home network. By contrast, the IP address visible to a website is the source IP address as seen from the internet side.
These two may match, but on home Wi-Fi and workplace networks they often do not.
For example, even if your home PC shows 192.168.1.10, that does not necessarily mean a website sees 192.168.1.10. Usually, an outside website sees the outside IP address used by the router or the access line.
What a private IP address is
A private IP address is an IP address reserved for use on inside networks such as homes, workplaces, and organizational networks.
The typical private IPv4 address ranges are as follows.
Range
Notation
Common example
10.0.0.0 to 10.255.255.255
10.0.0.0/8
10.0.0.5
172.16.0.0 to 172.31.255.255
172.16.0.0/12
172.16.1.20
192.168.0.0 to 192.168.255.255
192.168.0.0/16
192.168.1.10
Home routers often use IP addresses such as 192.168.0.x or 192.168.1.x.
These private IP addresses are used to identify devices inside a home or workplace. However, they are usually not used as destinations on the internet as-is.
In other words, even if there is a device with the IP address 192.168.1.10 in your home, someone from another place on the internet cannot simply specify 192.168.1.10 and directly access that device. Similar private IP addresses are reused in homes and workplaces around the world.
What a global IP address is
A global IP address is an IP address used on the internet.
Devices and lines that communicate on the internet, such as websites, mail servers, and DNS servers, use IP addresses that can be identified from outside.
In a home network, even if smartphones, PCs, tablets, game consoles, and similar devices each have private IP addresses, outside websites may see them as accessing from the same global IP address.
This is because the devices are not directly going out onto the internet, but communicating through a router.
The difference between the IP displayed on a device and the IP visible to a website
Suppose a PC inside a home is assigned the following IP address.
192.168.1.10
This is the PC's IP address on the home network.
When this PC accesses a website, what the website normally sees is not 192.168.1.10. In many cases, what the website sees is the outside IP address on the router or access-line side.
Where you look
Visible IP address
Meaning
Network settings on a PC or smartphone
192.168.1.10, etc.
The device's IP on the home network
Inside of the router
192.168.1.x, etc.
IP used to manage devices inside the home
Outside of the router or access line
Global IP, etc.
IP used for communication with the internet side
Website side
Outside IP
IP likely to be recorded as the source of access
The important point here is that IP addresses include an "IP as seen from the inside" and an "IP as seen from the outside."
Looking only at the IP address displayed on the device is not enough to judge how you appear to a website.
What NAT is
NAT stands for Network Address Translation. It is a mechanism for translating network addresses.
In a home network, inside devices are assigned private IP addresses. But when they go out to the internet, the router communicates using an outside IP address.
At that time, the router translates communication that left the inside device into outside communication, and returns the response that comes back to the correct device.
For example, suppose the following devices exist inside a home.
Device
Private IP inside the home
IP likely to be visible to a website
PC
192.168.1.10
Outside IP
Smartphone
192.168.1.11
Outside IP
Tablet
192.168.1.12
Outside IP
Inside the home, the PC, smartphone, and tablet have different private IP addresses.
But from an outside website's perspective, those devices may appear to be accessing from the same outside IP.
NAT manages a communication mapping table
With NAT, the router maps inside devices to outside communication.
For example, when a PC accesses a website, the router manages that communication as "this communication started from the PC at 192.168.1.10." Then it returns the response from the website to the correct PC.
If a smartphone accesses another website, the router manages that as separate communication.
In NAT commonly used by home routers, the mapping often includes not only IP addresses but also TCP or UDP port numbers.
This lets the router distinguish "which response should be returned to which device" even when multiple devices use the same outside IP.
Strictly speaking, this mechanism that maps multiple inside IP addresses to one outside IP address and multiple port numbers may be called NAPT or PAT. However, in everyday explanations, this is also often grouped under NAT.
Multiple devices can share one outside IP
With NAT, multiple devices inside a home can share one outside IP to access the internet.
For example, even if a PC and smartphone connected to the same Wi-Fi each access different websites, from the website side they may appear to be communicating from the same outside IP.
With this mechanism, all devices inside a home can use the internet without each having its own separate global IP address.
Because IPv4 has a limited number of available addresses, private IP addresses and NAT are widely used in home networks and organizational networks.
Outside parties cannot necessarily enter home devices directly
In an environment using NAT, inside home devices can start communication to the outside.
On the other hand, starting direct communication from outside to a device inside the home usually cannot be done as-is.
The reason is that the router does not have a mapping that says "which inside device should receive this communication that came from outside."
However, this does not mean "completely safe." Risk changes depending on router settings, device settings, the applications in use, vulnerabilities, login state, and similar factors.
NAT can sometimes make it harder for outside communication to pass through as a result, but its original purpose is not anonymization or defense itself. Its purpose is to map inside and outside communication.
NAT is not an anonymization technology
With NAT, a private IP address of a home device may not be directly visible to an outside website.
However, NAT is not an anonymization technology.
The main role of NAT is to map inside private IP addresses to outside communication. It is not a mechanism for hiding identity.
Websites and services may retain the outside IP address, access time, browser information, OS information, s, login information, account information, and similar data.
Also, even when the same outside IP is shared, the service side may be able to distinguish devices or users through Cookies, login state, and similar information.
For that reason, "the private IP is not directly visible to the website" and "you can communicate anonymously" are separate matters.
NAT may also happen on the access provider side
The outside side of a home router is not always assigned a global IP dedicated to that user.
NAT may also be performed further upstream by the access provider. In this case, the outside IP displayed in the home router's management screen may not match the IP visible to a website.
This mechanism is called CGNAT.
However, the important point to keep here is simple.
The IP displayed on the device, the router's outside IP, and the IP visible to a website are not always the same.
Summary
Devices in homes and workplaces may be assigned private IP addresses.
Private IP addresses are used to identify devices inside home and workplace networks. Typical ranges include 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.
By contrast, what external services such as websites see is often not the device's private IP, but the outside IP on the router or access-line side.
NAT is a mechanism that maps inside devices to outside communication. In home routers, it often maps not only IP addresses but also port numbers so that multiple devices can share one outside IP.
However, NAT is not an anonymization technology.
The important distinctions are as follows.
Item
Meaning
Caution
Private IP
IP used inside homes and workplaces
Usually not directly visible to websites
Global IP
IP used on the internet
Often visible to websites as the source of access
NAT
Mechanism for mapping inside and outside communication
Not a mechanism for anonymization
NAPT/PAT
Mechanism for distinguishing communication from multiple devices using IP addresses and port numbers
Commonly used in home routers
The IP address displayed on a device and the IP address visible to a website may be different.
Understanding this difference makes it easier to accurately organize how home networks and the internet side see communication.