A public IP address is an IP address that your home or business router receives from your ISP and is used when you access the internet. Public IP addresses are required for any publicly accessible network hardware such as a home router and the servers that host websites.
What Does a Public IP Address Do?
Public IP addresses differentiate the devices that are plugged into the public internet. Each device that accesses the internet uses a unique IP address. A public IP address is sometimes called an Internet IP.Miguel Co / Ach5
It's this address that each internet service provider uses to forward internet requests to a specific home or business, similar to how a delivery vehicle uses a physical address to forward packages to your house.
Think of your public IP address as any other address you have. For example, your email address and your home address are unique to you, which is why sending mail to those addresses ensures that messages get to you and not someone else.
The same exclusivity is applied to your IP address so your digital requests are sent to your network and not another network.
Private vs. Public IP Addresses: What's the Difference?
A private IP address is, in most ways, the same as a public IP address. It's a unique identifier for all the devices behind a router or other device that serves IP addresses.
With private IP addresses, the devices in your home can have the same private IP addresses as your neighbor's devices, or anyone else's all around the world. This is because private addresses are non-routable—hardware devices on the internet are programmed to prevent devices with a private IP address from communicating directly with any other IP beyond the router that they're connected to.
Because these private addresses are restrained from reaching the internet, you need an address that can reach the rest of the world, which is why a public IP address is needed. This type of setup enables all the devices in your home network to relay information back and forth between the router and ISP using a single address (a public IP address).
Another way to look at this is to think of the router in your home as an internet service provider. The router serves private IP addresses to the devices privately connected behind your router, an ISP delivers public IP addresses to the devices that are publicly connected to the internet.
Both private and public addresses are used for communication, but the range of that communication is limited based on the address that's used.
When you open a website from your computer, the request is sent from the computer to the router as a private IP address, after which the router requests the website from your ISP using the public IP address assigned to your network. Once the request has been made, the operations are reversed: the ISP sends the address of the website to your router, which forwards the address to the computer that asked for it.
Private and Public IP Address Ranges
Certain IP addresses are reserved for public use and others for private use. This is what makes private IP addresses unable to reach the public internet because they aren't able to communicate properly unless they exist behind a router.
The following ranges are reserved by the Internet Assigned Numbers Authority (IANA) for use as private IPv4 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
Excluding the addresses above, public IP addresses range from 1 to 191.
The 192.x.x.x addresses aren't registered publicly, which means they can only be used behind a router as private IP addresses. This range is where most private IP addresses fall, which is why the default IP address for most Linksys, D-Link, Cisco, and NETGEAR routers is an IP within this set, such as 192.168.1.1.
IPv6 address space is so large that the need for a private IP isn't in demand. However, there is a special unique unicast IP range of fc00::/7. This range is global, though.
How to Find Your Public IP Address
You don't need to know your public IP address most of the time, but there are situations where having it is important or even necessary, like to access your network, or a computer within it when you're away from home or your business.
The most basic example would be when you're using a remote access program. If you're in a hotel room in Shanghai, but need to "remote in" to your computer at home in Denver, you'll need to know the internet-accessible IP address (the public IP address your home router uses) so you can instruct that software to connect to the right place.
It's easy to find your public IP address. Use the Ach5 System Info Tool to see yours right now:
Although it's not quite as easy as a single click with this tool, you can also find your public IP through the router administration page. You'll need to log in to your router to do that.
The catch with both methods, assuming you're after this information for remote access reasons, is that you'll need to do this from your home computer or another device. If you're away, have a friend or co-worker do it for you. You could also use a DDNS service, some of which are even free. No-IP is one example, but there are others.
Why Public IP Addresses Change
Most public IP addresses change, and relatively often. Any type of IP address that changes is called a dynamic IP address.
When ISPs were new, users connected to the internet for only a short amount of time and then disconnected. An IP address that was used by one customer would then be open for use by another that needed to connect to the internet.
This way of assigning IP addresses meant that the ISP didn't need to purchase a large number of addresses. This general process is still in use today even though most people are always connected to the internet.
However, most networks that host websites have static IP addresses because they want to make sure that users have constant access to their server. Having an IP address that changes would defeat the purpose, as DNS records would need to be updated once the IP changes, which might cause unwanted downtime.
Home networks, on the other hand, are assigned dynamic IP addresses for the opposite reason. If an ISP gave a home network an unchanging address, it's more likely to be abused by customers who host websites from home, or by hackers who can try the same IP address over and over until they breach a network.
This is one reason why having a static IP address is more expensive than having a dynamic IP address. DDNS services are a way around this to some degree.
Another reason most networks have public IP addresses that change is that static IP addresses require more management, and therefore normally cost more for a customer to have than a dynamic one. For example, if you were to move to a new location a few miles away, but use the same ISP, having a dynamic IP address assignment would simply mean that you'd get another IP address that's available from the pool of addresses. Networks that use static addresses would have to be re-configured to apply to their new location.
Hiding Your Public IP Address
You can't hide your public IP address from your ISP because all of your traffic has to move through them before reaching anything else on the internet. However, you can hide your IP address from the websites you visit, as well as encrypt the data transfers (thus hiding traffic from your ISP), by first filtering your data through a virtual private network (VPN).
Normally, when accessing a website, that website can see that your specific public IP address requested to view their website. Doing a quick search on an IP finding website would tell that website who your ISP is. Since your ISP knows which IP addresses have been assigned to you, specifically, would mean that your visit to the website could be pinned directly to you.
Using a VPN service adds another ISP at the end of your request before you open another website. Once connected to a VPN, the same process as above takes place, only this time, instead of the website seeing the IP address that your ISP has assigned to you, they see the IP address that the VPN has assigned.
Here's an example of Google displaying a public IP address before and after a VPN is used:
In this example, if Google wanted to identify you, they would request that information from the VPN service instead of from your ISP, because again, that's the IP address they saw access their website.
At this point, your anonymity hinges on whether the VPN service is willing to give up your IP address, which of course reveals your identity. The difference between most ISPs and most VPN services is that an ISP is more likely to be required by law to tell who accessed the website, while VPNs sometimes exist in countries that have no such obligation.
There are several free and paid VPN services that offer different features. Looking for one that never saves traffic logs may be a good start if you're concerned that your ISP is spying on you.
A few free VPN services include FreeVPN.me, Hideman, Faceless.ME, and Windscribe VPN.
More Information on Public IP Addresses
Routers are assigned one private address called the default gateway IP address. In a similar fashion to a home network that has one IP address that communicates with the public internet, a router has one IP address that communicates with other connected private networks.
While it's true that the authority to reserve IP addresses rests with IANA, they are not some sort of central source for all internet traffic. If an outside device is breaching your network, it has nothing to do with IANA.