IPv6 is often summarised as “IPv4 with bigger addresses”. That’s true, but the bigger addresses change how networks are designed and how devices behave. Here’s what’s actually different.
At a glance
| IPv4 | IPv6 | |
|---|---|---|
| Address length | 32 bits | 128 bits |
| Notation | 192.0.2.1 |
2001:db8::1 |
| Total addresses | ~4.3 × 10⁹ | ~3.4 × 10³⁸ |
| Typical LAN size | /24 (254 hosts) | /64 (1.8 × 10¹⁹ addresses) |
| Address sharing | NAT is the norm | Every device can be globally addressable |
| Autoconfiguration | DHCP | SLAAC and/or DHCPv6 |
| Broadcast | Yes | No — multicast instead |
| Header | Variable, with checksum | Fixed 40 bytes, no checksum |
Addresses and notation
IPv4 addresses are four decimal octets. IPv6 addresses are eight groups of hexadecimal digits, and long runs of zeros are compressed with ::. 2001:0db8:0000:0000:0000:0000:0000:0001 and 2001:db8::1 are the same address. The IPv6 guide has an interactive explorer if you want to see the rules applied.
Numbering networks
IPv4 is scarce, so networks are sized tightly: a /24 for a small office, a /29 for a handful of servers. IPv6 turns this around. Every LAN gets a /64, regardless of how many devices it has, and a site typically receives a /48 or /56 — enough for thousands of subnets. Planning is about structure, not conserving addresses.
NAT and end-to-end connectivity
Because IPv4 addresses ran out, almost every home and many mobile networks use NAT; carrier-grade NAT puts many customers behind one public address. NAT breaks the end-to-end model: inbound connections, peer-to-peer apps and some games need workarounds.
IPv6 doesn’t need NAT. Devices have globally routable addresses, and a stateful firewall — which blocks unsolicited inbound traffic just as NAT did implicitly — provides the protection.
How devices get addresses
IPv4 relies on DHCP. IPv6 devices can configure themselves with SLAAC: the router advertises the /64 prefix and each device builds its own address. Modern systems use random, regularly changing interface identifiers so the address can’t be used to track a device across networks.
Is IPv6 faster or more secure?
Neither protocol is inherently faster, but IPv6 often avoids carrier-grade NAT, which can reduce latency. Security is comparable: IPsec exists for both, and what matters in practice is firewall configuration — which many networks forget to apply to IPv6.
Dual stack
The internet is in a long transition. Most networks run dual stack — both protocols at once — and browsers use “Happy Eyeballs” to prefer IPv6 while falling back to IPv4 quickly. Some mobile networks are IPv6-only and reach IPv4 services through NAT64.
You can check whether your connection has both on the homepage, and see how any IPv4 address is represented inside IPv6 with the IPv4 to IPv6 tool.