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IPv4 vs IPv6: what is the difference?
In short: IPv4 has about 4.3 billion addresses and relies on NAT to cope with the shortage. IPv6 has a practically unlimited number, removes broadcasts, supports automatic addressing and runs alongside IPv4 on most networks today.
IPv4 vs IPv6 in one sentence
IPv4 is the original internet addressing system with 32-bit addresses, while IPv6 is its successor with 128-bit addresses and a simpler design.
Side-by-side comparison
| Feature | IPv4 | IPv6 |
|---|---|---|
| Address length | 32 bits | 128 bits |
| Written as | 192.168.1.10 (decimal) | 2001:db8::10 (hexadecimal) |
| Number of addresses | About 4.3 billion | About 3.4 × 1038 |
| NAT | Widely needed | Not needed for address shortage |
| Broadcast | Yes | No; uses multicast instead |
| Auto-configuration | DHCP | SLAAC and/or DHCPv6 |
| Address resolution | ARP | Neighbor Discovery (NDP) |
| Header | Variable, has a checksum | Fixed 40 bytes, simpler |
What is IPv4?
IPv4 has carried the internet since the 1980s. Its addresses ran out at the regional registries years ago, which is why homes and offices use private addresses behind NAT.
What is IPv6?
IPv6 was designed to replace IPv4. Every device can have a global address again, routers do less work per packet, and devices can configure themselves with SLAAC. Most large providers, mobile networks and cloud platforms already support it.
Which one should you use?
In practice you run both (dual stack). New networks should plan IPv6 from the start, and security rules must cover IPv6 too: a firewall that only filters IPv4 leaves a gap. For exams, practise compressing and expanding IPv6 addresses; our free IPv6 tool helps.
Common mistakes and myths
- Ignoring IPv6 because "we do not use it": many devices have it switched on by default.
- Thinking IPv6 has no NAT means no security. A stateful firewall still protects the network.
- Forgetting that :: can appear only once in an address.
Learn more
Key takeaways
- IPv4 is 32-bit; IPv6 is 128-bit.
- IPv6 removes broadcasts and the need for NAT.
- Most networks run both (dual stack).
- Firewall policies must include IPv6.
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