An IP address (Internet Protocol address) is a unique numerical label assigned to every device connected to a computer network. Think of it as your device's digital postal address — just as physical mail is delivered to a street address, data packets on the internet are routed to your IP address.
Without IP addresses, the internet as we know it would be impossible. Every time you load a webpage, send an email, or stream a video, IP addresses are working behind the scenes to route information between the correct sender and receiver. The IP system is governed by the Internet Protocol, defined in RFC 791 (IPv4) and RFC 2460 (IPv6).
There are currently two versions of IP in active use: IPv4 (the legacy standard) and IPv6 (the modern replacement). Both coexist on today's internet through a technique called dual-stack networking.
IPv4 (Internet Protocol version 4) is the most widely used IP format. It represents addresses as four groups of numbers separated by dots, with each group (called an octet) ranging from 0 to 255.
Each IPv4 address is a 32-bit binary number. When written in dotted-decimal notation (like 192.168.1.1), each of the four octets represents 8 bits. This gives a theoretical maximum of 2³² = 4,294,967,296 unique addresses (about 4.3 billion).
When the internet was designed in the 1970s, 4.3 billion addresses seemed more than sufficient. The explosive growth of smartphones, IoT devices, and cloud servers meant the available IPv4 pool was nearly exhausted by 2011. Regional Internet Registries (RIRs) like RIPE NCC and ARIN ran out of unallocated IPv4 addresses, pushing adoption of IPv6.
Historically, IPv4 addresses were divided into classes A, B, and C for allocation to organisations of different sizes. This classful system has been replaced by CIDR (Classless Inter-Domain Routing), which allows more flexible prefix lengths like /24 or /16.
| Class | Range | Default Prefix | Typical Use |
|---|---|---|---|
| A | 1.0.0.0 – 126.255.255.255 | /8 | Very large organisations |
| B | 128.0.0.0 – 191.255.255.255 | /16 | Medium organisations |
| C | 192.0.0.0 – 223.255.255.255 | /24 | Small organisations |
IPv6 (Internet Protocol version 6) uses 128-bit addresses displayed as eight groups of four hexadecimal digits separated by colons. It provides approximately 340 undecillion unique addresses (3.4 × 10³⁸) — enough for every grain of sand on Earth to have trillions of addresses.
IPv6 addresses can be shortened by removing leading zeros and replacing consecutive groups of zeros with ::. For example:
Beyond sheer address space, IPv6 introduces several improvements over IPv4:
Despite being standardised in 1998, global IPv6 adoption still sits around 40–50% as of 2025, with IPv4 remaining dominant due to the cost and complexity of migration.
A public IP address is globally unique and directly routable on the internet. Your home router receives a single public IP from your Internet Service Provider (ISP). This is the address that websites, servers, and remote services see when you connect to them. You can look up your public IP using tools like ip-tracker.eu.
Private IPs are used within local networks — your home Wi-Fi, office LAN, or a data centre's internal network. They are defined in RFC 1918 and are not routable on the public internet. Your router uses a process called NAT (Network Address Translation) to map your private IP to its public IP when communicating with the outside world.
The three reserved private IP ranges are:
| Range | CIDR | Common Use |
|---|---|---|
| 10.0.0.0 – 10.255.255.255 | /8 | Large corporate networks |
| 172.16.0.0 – 172.31.255.255 | /12 | Medium networks |
| 192.168.0.0 – 192.168.255.255 | /16 | Home routers (most common) |
A static IP address never changes. It is either manually configured on the device or permanently assigned by an ISP. Web servers, mail servers, VPN endpoints, and businesses that need consistent inbound connectivity use static IPs. DNS records (A and AAAA) point to static IPs — if the IP changed, the domain would stop resolving correctly.
Static IPs are more expensive from ISPs because they require manual allocation and management. They also present a slightly higher security risk since the address never rotates, making targeted attacks easier to sustain.
Most home internet connections use dynamic IPs, automatically assigned by the ISP's DHCP (Dynamic Host Configuration Protocol) infrastructure. The address may change when your router reboots, when your DHCP lease expires, or on the ISP's own schedule (often every 24 hours).
Dynamic IPs are cheaper to manage because ISPs can reuse addresses from disconnected customers. They also offer a small privacy benefit — your IP address rotates, making long-term tracking slightly harder (though not impossible via other means).
If you need to run a server at home but only have a dynamic IP, Dynamic DNS services automatically update a DNS hostname whenever your IP changes. Services like No-IP, DuckDNS, or Cloudflare DDNS can keep a domain pointing to your current IP.
IP address allocation follows a hierarchical structure managed by the Internet Assigned Numbers Authority (IANA). IANA allocates large blocks of addresses to five Regional Internet Registries (RIRs):
RIRs allocate smaller blocks to ISPs and large organisations, who then assign individual addresses to their customers and servers. This registry data is publicly accessible via WHOIS and RDAP lookups, allowing anyone to see who owns a given IP block.
IP addresses serve critical functions across the modern internet and in network administration:
Your public IP is assigned by your ISP and visible to the websites you visit. Use ip-tracker.eu and click "What is my IP?" for an instant lookup including geolocation and ISP information.
Look for "IPv4 Address" under your active network adapter.
Open 192.168.1.1 or 192.168.0.1 in your browser to access most home routers. Your public IP is shown on the status or WAN page.
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