In our technical articles we have frequently referred to IP addresses and we have used them both locally, within the local LAN network, and on the interface that allows access to the Internet (often it is the WAN port on the router). In short, A IP address public (IP stands for Internet Protocol) is a number that uniquely identifies a device (called host) connected to the Internet.
When any device appears on the network with its own public IP address, for example assigned by the telecommunications operator, it becomes potentially reachable by any other host in turn connected to the Internet.
What is an IP address: the most important aspects
There are both addresses Public IPs that private: the former, as mentioned previously, are used to reach a host remote connected to the Internet, establish communication and then start a data exchange. The addresses Private IPson the other hand, are classes of addresses used to identify systems connected to a LAN: these host they are not directly accessible from the Internet.
However, there are exceptions (we’ll talk about them briefly later) in which the same public IP address is shared between multiple people host.
In the case of public IP addresses, the first part of the address identifies the net while the second is the single host. This is why IP addresses are critical for routing and addressing on the Internet data packets: By examining the first part of the public address, a router can immediately determine the destination network for the data that needs to be transferred. Once you reach the subnet local destination, the second part of the public IP is used to convey the data packets to the correct host.
L’Internet Protocol (IP) in fact operates immediately above the physical layer, at the link layer (link) and on top of it are “supported” all the protocols that we continue to use today, more than 40 years after their invention, such as TCP, UDP and the most recent QUIC.
Seeing is believing: every time you connect to the network with your router, the telecommunications operator automatically assigns that device a public IP address. The operation is completed IP address assignment public, the router is immediately reachable via the Internet: hence the importance of carefully checking the router configuration and making sure not to expose ports and other information on the network.
Where and how to find the public IP address
By visiting one of the following websites, you can read the public IP address assigned by the provider Internet to your router. The same IP address is generally shared by all devices connected downstream using a mechanism called NAT (Network Address Translation): we have dedicated an entire in-depth study to this topic.
By opening the websites proposed below from a device such as a desktop, notebook or smartphone connected to the router, you will always read the same public IP address (provided that all devices are connected to the same local network):
- IPify
- IPinfo
- DNSoMatic
- Icanhazip
Some services (even those mentioned) or the popular Maxmind, return not only the public IP address but using various signals allows you to establish the geographic location of the user.
To immediately read the public IP from a window PowerShell you can type the following and press Enter:
In the place of ifconfig.me/ipin the command seen previously, you can replace one of the addresses of the sites indicated in the bulleted list proposed above.
Who owns an IP address
Try copying the public IP address returned by the services suggested above by pasting it into the DomainTools WHOIS search box. This is a WHOIS service that allows you to know which person a public IP address belongs to.
As seen in the example, the public IP address belongs to a class of addresses assigned to TIM/Telecom Europe. In this case it is a block made up of more than 131,000 IP addresses: that many addresses are included in the range specified in correspondence with internal.
La subnet mask o netmask which can be read next to the entry Route in the WHOIS response, it allows you to trace the exact range of assigned IPs. The subnet mask indicated after the slash (in the example it is 15) allows you to obtain the network to which the specified IP address belongs.
The IP addresses managed in each block
Try typing how much next to Route (it is not visible in the image but the information is present in the final part of the response proposed by the WHOIS service) on the IP Calculator site: you will see how many IP addresses are managed within the block to which the address assigned to your router belongs.
The public IP address assigned by the telecommunications operator can be obtained in the same way even when you are connected to the data network via your smartphone or any device equipped with modem 4G/5G.
Use IPinfo to extract information about any IP address on the fly
One of the services we suggested above is particularly good at providing feedback on each IP address. Not only your own, but also those used by third parties. This is IPinfo which, as can be seen by examining the information on the home page, also returns the mnemonic address or host namethe approximate geographical location, the name of the telecom operator, the city, the time zone, and so on.
For example, try typing one of the following URLs into the address bar (replace <indirizzo_IP> with the public IP address that needs to be verified):
ipinfo.io/<indirizzo_IP>/jsonshows the list of information that can be extractedipinfo.io/<indirizzo_IP>/locreports the geographical location of the indicated hostipinfo.io/<indirizzo_IP>/orgreturns the name of the company to which the public IP belongsipinfo.io/<indirizzo_IP>/cityreports the city from which the specified IP address is usedipinfo.io/<indirizzo_IP>/regionindicates the region to which the IP corresponds
After registering on IPinfo, you can also check via API (Application Programming Interface), for example, if an IP address belongs to a VPN or the Tor network.
Sharing your public IP address among multiple users
Depending on the configuration used by the Internet provider, however, the same public IP address could be shared among multiple users. Lo schedule NAT it could therefore be used not only within the LAN network but also on the Internet access provider side.
In another article we presented solutions such as CGNAT and MAP-T used to extend the life of IPv4 addresses and which involve the sharing of the same public IP between multiple subscribers.
In another article of ours we talk about the difference between IPv4 and IPv6 addresses. Although the IPv4 addresses are still predominantly used, especially in local networks, the IPv6 addresses they can be exploited both on the Internet and in the LAN environment.
In the article My IP: how to find it and what it is for we saw that modern operating systems have long been ready for support IPv6a protocol which, by structuring addresses in 128 bits instead of 32 bits, as happens with the “traditional” IPv4, makes it possible to make up for the shortage of “old-fashioned” addresses.
The four numbers separated by dots (for example 8.8.8.8 is the address of a Google DNS server) are IPv4; those separated by colons (:) are IPv6 (example: 2001:4860:4860::8888also corresponding to the Google DNS server).
However, not all telecommunications operator networks currently support IPv6 (try carrying out this test).
Private IP addresses: what are they for?
When installing a router, the device usually receives a public IP address from the telecommunications operator while all devices connected downstream of the router (via Ethernet cable or in WiFi mode) use a private IP address.
Within the local LAN network, each device is always assigned a unique private IP: it cannot be the same, to avoid conflicts, as the one used by other hosts connected to the same network. Private IPs are usually assigned by a DHCP server (usually always running on the router but in…