What Is an IP Address
Every device connected to the internet is assigned a unique identification number. This is an IP address (Internet Protocol Address). Just as a postal address is needed to deliver a letter, an IP address is essential for routing data accurately across the internet.
When you browse a website, your browser sends a request to a server, and the server returns its response to your device. The mechanism that makes this exchange possible is the IP address. It is, in essence, the foundational technology underpinning all internet communication.
An IP address is more than just a number - it reflects the very design philosophy of the internet. For a deeper exploration of this concept, see our article on what an IP address really is. The packet-switching method adopted by ARPANET in the 1970s splits data into small packets, attaches a destination IP address to each one, and transmits them independently. This decentralized design is what has sustained the internet's resilience and scalability.
IPv4 and IPv6 - Two Generations
Two generations of IP addresses coexist on today's internet.
IPv4: Features and Limitations
Defined in 1981, IPv4 uses a format of four numbers separated by dots, such as "192.168.1.1." Its 32-bit address space can represent roughly 4.3 billion addresses. While that seemed ample at the time, the explosive growth of the internet turned address exhaustion into a real-world problem. IANA's unallocated address pool was depleted in February 2011, and APNIC - the registry for the Asia-Pacific region - ended routine allocations in April of the same year.
As of 2025, all five Regional Internet Registries (RIRs) have exhausted their routine IPv4 allocations. New addresses can only be obtained through transfer markets or the reallocation of returned blocks. Transfer prices hover around $30–50 per address, making the scarcity economically tangible. This exhaustion is a driving force behind the spread of CGNAT and the transition to IPv6.
The Solution IPv6 Brings
Designed as IPv4's successor, IPv6 uses hexadecimal notation with colons, such as "2001:0db8:85a3::8a2e:0370:7334." Its address space of roughly 340 undecillion addresses is, for all practical purposes, infinite. Beyond eliminating the exhaustion problem at its root, IPv6 also represents a major advance in security, with native support for encrypted communication via IPsec. For those looking to deepen their understanding, books on TCP/IP networking fundamentals provide thorough coverage of both protocol generations.
However, IPv6 comes with privacy considerations. Addresses generated through SLAAC (Stateless Address Autoconfiguration) may contain information derived from the device's MAC address, potentially enabling cross-network device tracking. To address this, "temporary addresses (Privacy Extensions)" defined in RFC 8981 are enabled by default on major operating systems, using randomly generated addresses that change periodically for external communication.
IPv6 Adoption Trends in 2024–2025
According to Google's statistics, global IPv6 adoption has reached approximately 45% as of 2025. In Japan, major ISPs have advanced their support, and IPv6 is the default for connections through NTT East/West's NGN network. While adoption exceeds 70% in India and France, it remains around 10% in China and Russia, highlighting significant regional disparities. IPv4 still dominates in some corporate internal networks and IoT devices, and a complete transition will take more time. For a deeper dive into how IPv6 works, see our IPv6 detailed guide.
Global IP and Private IP
IP addresses are broadly divided into two categories based on their role.
Global IP Addresses
These are addresses that are uniquely identifiable on the internet. Assigned by your ISP (Internet Service Provider), they enable communication from anywhere in the world. The address displayed on the IP Check-san homepage is your global IP address.
Private IP Addresses
These addresses are valid only within a local network, such as a home or office. A router uses NAT (Network Address Translation) to bridge private and global IP addresses. The typical private IP ranges are:
- 10.0.0.0 – 10.255.255.255 (Class A)
- 172.16.0.0 – 172.31.255.255 (Class B)
- 192.168.0.0 – 192.168.255.255 (Class C)
The Spread and Impact of CGNAT
As IPv4 addresses have become scarce, many ISPs have adopted CGNAT (Carrier-Grade NAT). To understand why NAT became so essential, see our article on how NAT saved the internet. Under CGNAT, multiple subscribers share a single global IP address, making it impossible for external parties to distinguish individual users. As of 2024, the majority of mobile connections and some fixed-line connections operate under CGNAT. While this approach conserves IP addresses, it introduces trade-offs - restrictions on P2P communication, online game hosting, and certain VoIP services. In a CGNAT environment, services requiring port forwarding cannot be self-hosted, necessitating alternatives such as cloud services or VPN tunnels for accepting inbound connections.
Dynamic IP and Static IP
IP address assignment comes in two flavors: dynamic and static. This distinction affects everything from everyday internet use to server operations and privacy protection.
Dynamic IP Assignment by ISPs
Most residential internet connections use DHCP (Dynamic Host Configuration Protocol), through which the ISP dynamically assigns IP addresses. Each time a router connects to the ISP, an address is automatically selected from the available pool. After a lease period expires or the router is restarted, a different address may be assigned. For ISPs, this is a cost-effective approach that allows limited IPv4 addresses to be efficiently shared among many subscribers.
When a Static IP Is Needed
On the other hand, a fixed IP address is required for use cases such as:
- Running web or mail servers - a fixed IP must be set in the DNS A record
- Building a VPN server - users cannot connect if the server's IP address changes
- IP-based access control - restricting access to internal systems to specific IP addresses
- Security cameras and remote desktop - requiring a consistent address for external connections
Static IPs are typically offered as a business service or a paid add-on for individual plans.
Privacy Implications
Dynamic IPs change periodically, making long-term behavioral tracking more difficult. In contrast, a static IP always uses the same address, allowing websites to easily identify visiting patterns by analyzing access logs. If you need a fixed IP for server operations or remote access, combining it with a VPN can mitigate privacy risks. You can infer whether you have a dynamic or static IP by checking the IP Check-san homepage at different times.
What Information Can Be Read from an IP Address
Using an IP address as a starting point, the following information can be estimated:
- Approximate geographic location (country, region, and city level)
- The ISP being used
- AS number (Autonomous System Number)
- Connection type (fixed-line, mobile, etc.)
This information is widely used for access control and regional content optimization in web services. For example, video streaming services serve different content by country based on licensing, and e-commerce sites automatically switch currencies and languages - all powered by IP-based geolocation behind the scenes.
However, it is important to emphasize that it is impossible to determine a person's exact home address or name from an IP address alone. While GeoIP database accuracy is high at the country level (95–99%), it drops to around 50–80% at the city level, with typical errors ranging from several kilometers to tens of kilometers. Accuracy varies greatly by country and region - it tends to be relatively high in countries like Japan with well-developed ISP infrastructure, but may be limited to country-level identification in developing nations. Under CGNAT or mobile connections, the ISP's relay point location is often returned, which can differ significantly from the user's actual location. For more on how IP-based geolocation works and its accuracy, see our GeoIP article.
Common Misconceptions About IP Addresses
Can Individuals Really Be Identified by IP Address?
In TV dramas and movies, investigators often pinpoint a suspect's location instantly from an IP address. In reality, however, an IP address alone cannot identify an individual. An IP address reveals only the ISP and a rough geographic area. To trace it to a specific person, the ISP's subscriber records must be cross-referenced - a process that requires legal procedures such as a court order.
Furthermore, in CGNAT environments where dozens to hundreds of users share the same IP address, it is technically challenging to establish a one-to-one correspondence between an IP address and a subscriber. For law enforcement to trace specific communications, supplementary information such as port numbers and timestamps is essential in addition to the IP address.
The Overconfidence in "VPNs Make You Completely Anonymous"
A VPN is an effective tool for hiding your IP address, but tracking through channels other than IP - such as browser fingerprinting, cookies, and DNS leaks - remains possible. WebRTC leaks in particular are an often-overlooked risk where your real IP address can be exposed through the browser's WebRTC functionality even while using a VPN. Achieving stronger anonymity requires combining multiple countermeasures. For details on DNS leak mechanisms and countermeasures, see our DNS leak article.
How to Check Your IP Address
There are several ways to check your IP address, but the easiest is to use a web tool like IP Check-san.
- Visit the IP Check-san homepage (GeoIP information and ISP details are displayed simultaneously)
- Run
ipconfig(Windows) orifconfig(macOS/Linux) in a command prompt or terminal - Check the WAN-side IP address from your router's admin panel
In addition to IP address lookup, IP Check-san calculates a security score and evaluates browser fingerprint uniqueness. The security score comprehensively assesses your connection protocol, DNS leak status, WebRTC leak status, and more, providing a numerical indicator of how secure your current connection is. The fingerprint feature analyzes how unique the combination of your browser settings and environment information is, offering a metric for tracking susceptibility.
Practical Uses of IP Check-san
- Instantly verify whether your VPN connection is working correctly by checking for IP address changes
- Identify weaknesses in your connection environment using the security score and prioritize countermeasures
- Check fingerprint uniqueness and compare how browser setting changes affect tracking risk
- Experience firsthand how much location information can be inferred from your IP address via the GeoIP display
- Confirm your IPv4/IPv6 connection status and determine whether your ISP supports IPv6
- If you're curious about what your connection speed numbers actually mean, our guide on internet speed units breaks down the terminology
IP Addresses and Privacy
When combined with web browsing history, an IP address can serve as a clue for tracking user behavior patterns. Consulting a guide to internet privacy protection can help you understand the full scope of these risks. The following measures are effective for addressing this risk:
- Use a VPN to conceal your IP address
- Enhance anonymity with the Tor browser
- Route traffic through a proxy server
- Block unnecessary traffic with a firewall
A VPN is a convenient and effective option, but because traffic is routed through a VPN server, connection speeds typically decrease by 10–30%. Additionally, if the VPN provider itself retains logs, anonymity is not absolute. It is important to balance convenience and privacy, choosing the right tool for each situation. For more on VPN types and protocol differences, see our VPN article. For anonymous communication using Tor, see our Tor browser article.
IP Addresses and Privacy Regulations
The legal status of IP addresses varies by country and region. Under the EU's GDPR (General Data Protection Regulation), IP addresses are explicitly defined as "personal data," and website operators need a legal basis to collect and process them. As of 2025, privacy legislation is advancing worldwide under GDPR's influence - Brazil's LGPD, Thailand's PDPA, South Korea's PIPA, and others increasingly treat IP addresses as personal information.
Under Japan's Act on the Protection of Personal Information, an IP address alone is not immediately classified as "personal information," but it may qualify if it can be easily cross-referenced with other data to identify an individual. The concept of "personal-related information" introduced in the 2022 amendment mandates obtaining consent when providing identifiers such as cookies or IP addresses to third parties for linking with personal data. For website operators, clearly stating the retention period and purpose of access logs has become more important than ever. For a comprehensive overview of privacy regulations, see our privacy laws article.
Beyond concealing your IP address, understanding how GeoIP-based location estimation works is also a first step toward privacy protection. Knowing how much information can be inferred from your IP address helps you choose appropriate countermeasures.
Actions You Can Take Right Now
After reading this article, follow these steps to assess the privacy risks associated with your IP address and consider countermeasures:
- Visit the IP Check-san homepage to check your global IP address
- Compare the displayed GeoIP information with your actual location - the more accurate it is, the easier it is for third parties to estimate your position
- Review your security score and confirm that no DNS leaks or WebRTC leaks have been detected
- Check your fingerprint uniqueness and evaluate whether you are in a state that is easy to track
- Verify whether you are connected via IPv6 (IPv6 addresses may contain device-specific information, requiring privacy considerations)
- Compare how your IP address and GeoIP information change with and without a VPN connection
- If you perceive elevated risk, consider adopting a VPN or reviewing your browser's privacy settings