IPv4 vs IPv6: What's the Difference?
IPv4 has 4.3 billion addresses and ran out in 2011. IPv6 has 340 undecillion. Formats, headers, NAT, adoption and dual-stack compared side by side.
Why we needed a second version
IPv4 (Internet Protocol version 4) dates from the early 1980s and has about 4.3 billion addresses. Plenty for a research network, not for a world of phones, cloud servers and Wi-Fi gadgets. The Internet Assigned Numbers Authority (IANA) handed its last IPv4 blocks to the Regional Internet Registries in February 2011. IPv6 exists so that never happens again.
IPv4: 32 bits, dotted decimal
An IPv4 address is 32 bits, written as four numbers from 0 to 255 with dots between them. 192.168.1.1 is 11000000.10101000.00000001.00000001 in binary.
- 232 = 4,294,967,296 addresses
- Header: 20 to 60 bytes, variable
- Both the sender and routers on the way can fragment packets
- Broadcast: yes. IPSec: optional
IPv6: 128 bits, hexadecimal
An IPv6 address is 128 bits, written as eight groups of four hex digits with colons between them:
2001:0db8:85a3:0000:0000:8a2e:0370:7334
Drop the leading zeros in each group, replace one run of all-zero groups with :: (once per address), and the same address becomes:
2001:db8:85a3::8a2e:370:7334
- 2128, roughly 3.4 × 1038 addresses
- Header: fixed 40 bytes, so routers process it faster
- Only the sender fragments packets
- No broadcast; multicast and anycast instead. IPSec: mandatory in the specification
Side by side
| Feature | IPv4 | IPv6 |
|---|---|---|
| Address length | 32 bits | 128 bits |
| Address format | Dotted decimal | Hexadecimal with colons |
| Address space | ~4.3 billion | ~340 undecillion |
| Header size | 20 to 60 bytes (variable) | 40 bytes (fixed) |
| IPSec | Optional | Built in |
| NAT required? | Yes (addresses are scarce) | No (every device gets a public IP) |
| Broadcast | Yes | No (uses multicast) |
| Auto-configuration | DHCP | SLAAC + DHCPv6 |
| Checksum in header | Yes | No (other layers handle it) |
| Fragmentation | Routers and sender | Sender only |
Adoption and dual-stack
As of 2025 roughly 40 to 45% of Google's traffic arrives over IPv6, with India, the United States, Germany and France among the leaders.
Most networks are mid-transition and run dual-stack: each device holds an IPv4 and an IPv6 address at once, so it can reach services that only speak one of the two. Where that is not an option:
- Tunneling (6to4, Teredo): wraps IPv6 packets inside IPv4 to cross an IPv4-only network.
- NAT64/DNS64: lets IPv6-only clients reach IPv4-only servers through a translator.
At home you do nothing; your operating system and ISP sort it out. If you run a service, make sure it answers over IPv6 too. IPv4 addresses only get scarcer and more expensive.
Try it on a real address. Free, no account needed.