IPv4 vs IPv6 — What's the Difference?

IPv4 vs IPv6 — the differences at a glance

Property	IPv4	IPv6
Address length	32 bits	128 bits
Address space	~4.3 billion	~340 undecillion (3.4 × 10³⁸)
Format	`192.168.1.1`	`2001:db8::8a2e:370:7334`
Notation	4 decimal octets	8 hex blocks of 16 bits
Header	variable, 20–60 bytes	fixed 40 bytes
Header checksum	yes	no (efficiency gain)
Fragmentation	routers may fragment	endpoint only
Broadcast	yes (`255.255.255.255`)	replaced by multicast
Auto configuration	needs DHCP	SLAAC built in
Encryption	optional (IPsec add-on)	originally mandatory, now optional
NAT typical	yes, almost everywhere	not required
QoS	ToS field (rarely used)	Traffic Class + Flow Label
DNS record type	A	AAAA
Adoption (2026)	~96 %	~46 % (in parallel)

To check whether you are currently on IPv4 or IPv6, use the IPv6 Test. The homepage shows both visible public addresses.

Why IPv6 at all?

One-line answer: we ran out of IPv4. The IANA pool was exhausted in 2011, the regional registries (RIPE in Europe, ARIN in North America) in 2015 / 2019. Providers have to recycle, buy, or hide multiple customers behind one address via Carrier-Grade NAT — the "one address per user" model of the early internet no longer works.

IPv6 solves this permanently: 2¹²⁸ addresses = 340 undecillion. Every grain of sand on Earth could get billions of IPv6 addresses without running out.

Format examples

IPv4:

192.168.1.1
93.184.216.34
8.8.8.8

IPv6 — full and shortened:

2001:0db8:0000:0000:0000:8a2e:0370:7334   (full)
2001:db8::8a2e:370:7334                    (shortened, :: replaces zero blocks)
fe80::1                                    (link-local)
::1                                        (loopback, equivalent to 127.0.0.1)
::ffff:93.184.216.34                       (IPv4-mapped, embedded in IPv6)

Address space, visualized

If 4 billion IPv4 addresses were a golf ball, the IPv6 address space is the size of the sun. That's not marketing — it's a real scale:

IPv4: 4 × 10⁹
IPv6: 3.4 × 10³⁸

The scaling factor is 8.5 × 10²⁸.

NAT: the workaround that made IPv6 less urgent

IPv4 only still fits today because Network Address Translation hides multiple devices (PC, phone, smart TV, IoT) behind a single public IP. Upsides of NAT:

Address savings
"Quasi firewall" — inbound connections can't reach internal devices without port forwarding

Downsides:

Port forwarding is painful for servers, VoIP, games
The internet's end-to-end principle is broken
CGNAT (provider-level NAT) makes it worse

IPv6 abandons NAT — every device gets its own global address. Security is then enforced at the endpoint or by the router firewall, not "by accident" via NAT.

Auto-configuration: SLAAC instead of DHCP

In IPv6 a device can compute its own address from the network prefix and its MAC (or a random Privacy Extension). No DHCP server needed — SLAAC (Stateless Address Autoconfiguration) handles it.

The result: plug-and-play on unknown IPv6 networks works better than on IPv4.

Performance

With proper config IPv6 is slightly faster (simpler header, no router fragmentation, multicast instead of broadcast). Real-world depends on backbone peering:

Cloudflare data: IPv6 often 10–30 % faster on mobile routes
Akamai measurements: lower round-trip on certain routes

But: if a provider peers IPv6 poorly, IPv6 can be slower. When in doubt, run the Speedtest once with and once without IPv6.

Security

Common myths corrected:

IPv6 is more secure. — Not automatically. The "NAT-quasi-protection" argument falls away, but every decent router blocks inbound IPv6 by default just like inbound IPv4 without port forwarding.
With IPv6 anyone can reach my device. — Only if the router firewall is disabled or misconfigured. Practically every modern home router with IPv6 support is inbound-default-deny.
IPv6 is more anonymous. — Actually the opposite without Privacy Extensions: the MAC is embedded in the IPv6 → device-precise tracking possible. On modern Windows, macOS, Linux, Privacy Extensions are default.

Should I enable or disable IPv6?

Leave it on, normally. Benefits:

Avoids CGNAT issues
Faster routes on many networks
Prerequisite for modern protocols (HTTP/3, ECH)

Disable only if:

Specific VPN software doesn't tunnel IPv6 cleanly → DNS/IP leak possible → verify with DNS Leak Test
Corporate tools only support IPv4

Current adoption

As of 2026 (Google statistics):

Global IPv6 reach: ~46 %
Germany: ~75 % (very high)
USA: ~52 %
Switzerland: ~55 %
France: ~76 %

Practical takeaway: if your ISP supports IPv6, you're almost certainly dual stack — running both in parallel. On most home connections this happens automatically.

IPv6 Explained — deep dive on migration
Subnet Mask Cheat Sheet (CIDR /8 to /32) — IPv4 reference
What is an IP address?
Public vs Private IP
Tools: IPv6 Test, DNS Leak Test, Speedtest
Glossary: IPv4, IPv6, NAT, SLAAC, CGNAT