What is an IP address, really?

Think of an IP address as a street address for devices. It's how computers, phones, smart TVs, and servers find each other on the network. Just like your house number helps mail reach your door, an IP address helps data reach the right device. That's it. No magic. Just an identifier that must be unique at the place it's used.

Every device that wants to communicate over the internet needs one of these addresses. When you send a message, browse a website, or stream a video, your device uses IP addresses to know where to send the data and where to expect responses back. It's the foundation that makes the entire internet work.

A brief history: why we have two systems

Back in the 1970s and early 1980s, when the internet was just an experimental network connecting universities and research institutions, nobody imagined it would grow to connect billions of devices. The original designers of IPv4 thought 4.3 billion unique addresses would be more than enough for any conceivable network.

They were brilliant engineers, but they couldn't predict smartphones, tablets, smart TVs, IoT devices, security cameras, and every appliance getting connected to the internet. By the 1990s, it became clear that we were going to run out of IPv4 addresses. The solution? Design a completely new addressing system with so many addresses that we'd never run out again. That's IPv6.

The transition from IPv4 to IPv6 has been happening gradually since the late 1990s. Today, both systems run side by side on the internet, and most modern devices support both. This dual approach ensures everything keeps working while the internet slowly migrates to the newer system.

Meet IPv4: the classic format

IPv4 is the one most people recognize: four numbers separated by dots, such as 203.0.113.7. Each number ranges from 0 to 255. Inside the machine, those four numbers are really just 32 ones and zeros (called "bits"). With 32 bits, you can count to about 4.3 billion. When IPv4 was designed, that felt enormous. Today, with billions of phones, laptops, IoT devices, and servers, 4.3 billion isn't enough—especially because many of those addresses are reserved, and we need globally unique ones for the public Internet.

Here's what makes IPv4 familiar and easy to understand: the numbers are in base 10 (the counting system we use every day), and the format is consistent. 192.168.1.1, 10.0.0.1, 172.16.0.1 — these all follow the same pattern. You can easily tell if two IPv4 addresses are similar just by looking at them.

The limitation isn't just about the total number available. IPv4 addresses are also distributed inefficiently. Large blocks were given out in the early days to organizations that didn't end up needing them all. Additionally, the way IPv4 networks are structured means that addresses can't always be used as efficiently as we'd like.

Meet IPv6: the big new address space

IPv6 uses 128 bits. That's a huge leap. If 32 bits is a small city, 128 bits is the galaxy. The number of IPv6 addresses is often written as 2128—an astronomically large figure. The goal of IPv6 is simple: ensure we never run out of addresses again and make modern networking features cleaner and more scalable.

To put this in perspective: IPv6 has enough addresses to give every grain of sand on Earth its own unique address, and still have plenty left over. It's not just "more addresses"—it's so many more addresses that we can be wasteful with them and still never run out. This abundance changes how we think about network design.

IPv6 was also designed to fix several issues with IPv4 beyond just address space. It includes better support for mobile devices, more efficient routing, built-in security features, and simpler network configuration. While IPv4 has been patched and extended over the decades, IPv6 was built from the ground up with decades of internet experience.

How they look on the screen

  • IPv4: dotted decimal, e.g., 192.0.2.25
  • IPv6: eight groups of hex numbers separated by colons, e.g., 2001:0db8:0000:0000:0000:0000:0000:0001. To save space, IPv6 lets you shorten runs of zeros: 2001:db8::1.

Hex is base‑16, so you'll see digits 0–9 and letters a–f. It's not scary—just another way to write numbers compactly. The letters a, b, c, d, e, and f represent the values 10, 11, 12, 13, 14, and 15 respectively.

The double colon (::) in IPv6 is a handy shortcut that means "one or more groups of all zeros." You can only use this shortcut once per address to avoid ambiguity. So 2001:db8:0000:0000:0000:0000:0000:0001 becomes 2001:db8::1. Much cleaner!

Leading zeros in each group can also be omitted. So 2001:0db8:0000:0042:0000:8329:0000:0001 can be written as 2001:db8:0:42:0:8329:0:1. These shortcuts make IPv6 addresses much more manageable in practice.

Private vs public addresses

With IPv4, home and office networks often use private ranges like 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16. Your router then uses Network Address Translation (NAT) to share one public IPv4 on the Internet. IPv6 works differently: most networks receive a block of public IPv6 addresses and assign them directly to devices—no NAT needed. There are special "unique local" ranges in IPv6 (like fc00::/7) for private use, but the normal pattern is to use global addresses with proper firewalling.

This difference is fundamental to how the two protocols work. In the IPv4 world, NAT became necessary because we didn't have enough addresses to go around. Your home router gets one public IPv4 address from your internet provider, then creates a private network behind it using addresses like 192.168.1.x. All your devices share that one public address through NAT translation.

IPv6 changes this completely. Your internet provider can give you thousands or millions of public IPv6 addresses (typically a /56 or /48 block). Each device in your home can have its own globally unique public address. This doesn't mean everything is exposed to the internet—you still use firewalls to control what connections are allowed.

Why IPv6 reduces the need for NAT

NAT became common because we ran low on IPv4 addresses. IPv6 gives enough space that every device can have its own public address. That can simplify troubleshooting (no more port‑forward rabbit holes) and enable peer‑to‑peer connections more easily. It doesn't mean "no security"—it means you rely on proper firewall rules instead of address hiding.

NAT creates complications that many people don't realize. When multiple devices behind a NAT router try to use the same service, the router has to keep track of which internal device each connection belongs to. This breaks some applications and makes it difficult to run servers or accept incoming connections. Online gaming, video conferencing, and peer-to-peer file sharing all work better without NAT.

With IPv6, instead of hiding devices behind NAT, you use stateful firewalls to control access. You can configure exactly which connections are allowed in and out, giving you the security benefits of NAT without the complications. Many network administrators find this approach cleaner and more predictable.

Subnetting: understanding prefixes

Both IPv4 and IPv6 use a prefix length to define how big a network is. You'll see this as "CIDR notation," like /24 or /64 appended to an address. The slash means "how many bits belong to the network part." The remaining bits are for hosts inside that network.

  • IPv4: A /24 means 24 of the 32 bits are the network (leaving 8 bits for hosts). That gives 256 total addresses, usually 254 usable hosts after excluding the network and broadcast addresses.
  • IPv6: A /64 is the standard size for a LAN. It leaves 64 bits for hosts—an unimaginably large number (264). You'll never run out of host addresses in a /64.

The prefix length determines how many devices can be on the same network segment and how networks are organized hierarchically. Shorter prefixes (like /16) create larger networks with more devices, while longer prefixes (like /30) create smaller networks with fewer devices.

Understanding prefixes is crucial for network design. In IPv4, you might use /24 for office networks (254 computers), /28 for small branches (14 computers), and /30 for point-to-point links between routers (2 addresses). In IPv6, /64 works for almost everything, which actually simplifies planning.

"First" and "last" hosts

In IPv4, networks have a "network address" (all host bits zero) and a "broadcast address" (all host bits one). Usable hosts normally start at network+1 and end at broadcast−1, except for tiny subnets like /31 or /32 where special rules apply. In IPv6, there's no broadcast, so every address in the range is technically usable; we still often show a "first" and "last" for convenience.

The broadcast address in IPv4 serves a specific purpose: when a device sends data to the broadcast address, every device on that network receives it. This is useful for certain network protocols but can also create traffic that affects all devices. IPv6 eliminates broadcast traffic, using more efficient multicast communication instead.

This difference means that IPv6 networks are inherently more efficient with network traffic. Instead of broadcasting messages to every device (whether they want them or not), IPv6 uses targeted multicast to send messages only to devices that have expressed interest in receiving them.

Reading an IPv6 without going cross‑eyed

Here's a trick. Split the address into eight hextets (groups of four hex digits). If you see ::, that's "some number of zero groups" squeezed down. Expand it to eight groups in your head, then look at the prefix length. A /64 means the first four hextets are the network, the last four are host space. For example, 2001:db8:abcd:1234::/64 has 2001:db8:abcd:1234 as the network part, and the remaining four groups can vary.

Practice makes this much easier. Start by looking at the structure: 2001:0db8:85a3:0000:0000:8a2e:0370:7334. The first part (before the :: if present) is usually the network portion. The last part is usually the device identifier. With time, you'll start recognizing common patterns and prefixes.

Many organizations use consistent patterns in their IPv6 addresses to make them easier to manage. For example, they might use 2001:db8:1:: for the first VLAN, 2001:db8:2:: for the second VLAN, and so on. This creates readable, predictable address schemes.

Real‑world deployment patterns

  • Dual stack: Most networks run IPv4 and IPv6 side‑by‑side. If IPv6 works, great. If not, IPv4 is the fallback. This is the most common path today.
  • IPv6‑only with NAT64/DNS64: Some modern networks run IPv6 only and translate when they must reach IPv4‑only destinations. Great for mobile networks and brand‑new environments.
  • Tunnels and transition tech: If you can't get native IPv6 from your ISP yet, there are tunnel brokers and cloud solutions that can help you experiment.

The transition to IPv6 is happening gradually because changing internet infrastructure is complex and expensive. Dual stack deployment allows organizations to add IPv6 support without breaking existing IPv4 services. This approach has been successful in maintaining internet stability during the transition.

Major internet services like Google, Facebook, and Netflix now serve significant portions of their traffic over IPv6. Mobile networks are leading the adoption because new deployments can be built IPv6-first without legacy constraints. Many mobile providers now deliver IPv6-only connections to phones, using translation only when accessing IPv4-only websites.

Performance and security differences

Performance isn't inherently better or worse with IPv6. What matters is routing, peering, and your ISP's implementation. On security: IPv6 is not "less safe." It's simply different. You still need a stateful firewall, sensible inbound rules, and good hygiene (patching, strong auth, least privilege).

Some performance characteristics do differ between the protocols. IPv6 headers are simpler and more efficient to process, which can provide small performance benefits in high-traffic scenarios. However, if your network or ISP has better IPv4 infrastructure, IPv4 might actually perform better for you right now.

From a security perspective, IPv6 includes IPSec support as a standard feature, while IPv4 had IPSec added later. However, in practice, most security happens at higher layers (HTTPS, VPNs, application security) rather than at the IP level. The fundamental security principles remain the same regardless of IP version.

Common myths, gently debunked

  • "IPv6 is only for big enterprises." Not true. Home routers, cloud VMs, phones—all support it. If your ISP offers it, you already have it.
  • "IPv6 replaces VLANs." Nope. VLANs segment L2 broadcast domains. IPv6 deals with addressing and L3 routing. They solve different problems.
  • "IPv6 breaks NAT security." NAT isn't a security control. Firewalls are. With IPv6 you keep using a firewall, you just don't need NAT to stretch addresses.
  • "IPv6 is slower." It can be faster, slower, or the same depending on routes. Measure, don't assume.
  • "IPv6 is too complicated." The addresses look intimidating at first, but the concepts are actually simpler than IPv4 in many ways. No NAT complications, no address exhaustion worries, more straightforward routing.
  • "Nobody uses IPv6 yet." Google reports that over 35% of their traffic now comes over IPv6, and major websites serve significant IPv6 traffic. Adoption is accelerating rapidly.

Picking the right prefix sizes (quick heuristics)

  • IPv4: Offices commonly use /24. Point‑to‑point links use /31. Tiny VLANs might use /28 or /29.
  • IPv6: LANs and VLANs should be /64. WAN links vary (/64 or /127 are both seen). ISPs often delegate a /56 or /48 to a site so you can carve multiple /64s.

The beauty of IPv6 address abundance is that you don't have to worry much about "wasting" addresses. In IPv4, you carefully calculate exactly how many devices you need and choose the smallest subnet that fits. In IPv6, you can be generous with address space and focus on creating clean, logical network designs.

Hands‑on: try a couple of examples

Open IP Prefix Calculator in a new tab and try:

  • 192.168.50.10/26 — See the network, broadcast, first/last hosts, mask, and host count.
  • 2001:db8:1234:5678::abcd/64 — See the network and host range in IPv6. Notice how the "total addresses" shows as a power of two.
  • 10.0.0.0/8 — One of the large private IPv4 ranges, with over 16 million addresses.
  • 2001:db8::/32 — A large IPv6 block that could be subdivided into 4 billion /64 networks.

Reading logs and tools output

When you enable IPv6, you'll start seeing IPv6 addresses in logs, firewall rules, cloud consoles, and traceroutes. Don't panic. It's the same idea as IPv4, just bigger numbers and colons. Your brain will adapt quickly. In fact, you'll start to prefer that you don't have to wrestle with NAT weirdness anymore.

Many network tools support both IPv4 and IPv6. Commands like ping become ping6, traceroute becomes traceroute6, and so on. However, modern versions of these tools often detect the address type automatically and use the appropriate protocol.

Log analysis becomes more straightforward in many ways with IPv6. Since there's no NAT, the source address in your logs is the actual device address, not a shared router address. This makes it easier to track user behavior and troubleshoot connectivity issues.

Frequently asked questions

Do I need to memorize hex? No. Recognize patterns: db8 shows up in documentation; :: collapses zeros; /64 is the standard LAN size.

Is IPv6 mandatory? The Internet is migrating over time. Supporting IPv6 future‑proofs your network and can improve reachability.

Will my apps break? Most modern apps and OSes are happy with IPv6. Test critical systems, but you'll be surprised how smooth it is.

When should I start using IPv6? If your ISP and equipment support it, there's no reason not to enable it alongside IPv4. Start experimenting in non-critical environments first.

What about DNS? IPv4 addresses go in A records, IPv6 addresses go in AAAA records. Most DNS servers and resolvers handle both automatically.

The migration timeline and what it means for you

The transition to IPv6 has been ongoing for over two decades, but it's accelerating rapidly. Major internet service providers now offer IPv6 by default, major websites support it, and most modern devices prefer it when available. However, IPv4 isn't going away anytime soon.

For most people and organizations, the best approach is dual stack: support both protocols and let the devices and networks choose the best option automatically. This provides the benefits of IPv6 where available while maintaining compatibility with IPv4-only resources.

If you're designing new networks or applications, plan for IPv6 from the start. It's much easier to build with IPv6 support than to retrofit it later. For existing systems, gradual migration with dual stack deployment is the safest approach.

Key takeaways

  • IPv4 = familiar, limited space, lots of NAT.
  • IPv6 = massive space, simpler end‑to‑end addressing.
  • Prefixes (/numbers) define network size in both worlds.
  • Firewalls matter in both; NAT is not a security feature.
  • Both protocols will coexist for years; dual stack is the practical approach.
  • IPv6 adoption is accelerating, especially in mobile and cloud environments.
  • The concepts are similar; mainly the notation and scale differ.

Your next step

Grab a couple of your real subnets and run them through the IP Prefix Calculator. Seeing your own data makes the concepts click. Start with your home network or a lab VLAN. Mix IPv4 and IPv6 tests. Notice how the outputs parallel each other—network, range, host count—and how much simpler IPv6 feels once you get used to the notation.

Bonus: quick IPv6 reading exercise

Take 2001:db8:ffee:42::beef/64. The network is 2001:db8:ffee:42::/64. The first "host" would be ...:42::1. The last would be ...:42:ffff:ffff:ffff:ffff (we usually show "last usable" as one less than the max for symmetry with IPv4). Try a /68 on the same base: 2001:db8:ffee:42::/68. You'll get sixteen /68s inside that /64; that's handy when you want to organize segments without leaving the comfortable /64 world.

That's all there is to it: two address families, same basic ideas, different scale. Once you stop fearing the colons, IPv6 becomes a friendly giant that solves real problems and makes network design cleaner and more scalable.