IPv4 vs IPv6: what's the difference?
IPv4 addresses are 32-bit numbers written like 190.60.10.1, with room
for about 4.3 billion in total; IPv6 addresses are 128-bit numbers written
like 2001:4860:4860::8888, with an address space so vast it is effectively
inexhaustible — trillions of addresses for every person alive — and both
versions are running side by side on today’s internet, often on the same
connection at once.
Address formats, and why IPv4 ran out
IPv4’s roughly 4.3 billion addresses sounded huge in the 1980s and ran out for real allocation over a decade ago, once phones, routers, set-top boxes, and IoT devices multiplied far past the number of people online. IPv6 fixes the shortage by brute force: a 128-bit address space so large that assigning entire address blocks per device, per household, or per country barely dents it. The trade-off is that providers who never had enough IPv4 to go around now lean on carrier-grade NAT, sharing one public IPv4 address across hundreds of customers, while rolling out IPv6 in parallel where a public address per device is normal again — though whether that address stays fixed or keeps rotating is a separate question, covered in our guide on static vs dynamic IPs. Network address translation (NAT) already stretches IPv4 further by letting an entire home share one public address among many devices, which is part of why the shortage never caused obvious outages — it was absorbed quietly at the router level for over a decade before CGNAT pushed the same trick up to the ISP.
Dual-stack: how your device picks
Most modern connections are “dual-stack”: your device gets both an IPv4 and an IPv6 address at once, and it decides per connection which to use. The usual algorithm, informally called Happy Eyeballs, tries IPv6 first because it is typically faster on a healthy dual-stack network, then falls back to IPv4 within a fraction of a second if IPv6 fails or is unavailable — the switch is invisible to you. You can see which one your own connection is actually using right now on the home page, which shows whichever address answered the request; a dedicated side-by-side dual-stack check that tests both at once is on our roadmap. You can also tell which family an address belongs to just by its shape: IPv4 addresses are four decimal numbers separated by dots, while IPv6 addresses are eight groups of hexadecimal digits separated by colons, often with a run of zeros abbreviated as a double colon.
Why adoption varies by country and carrier
IPv6 usage is uneven worldwide because upgrading requires both the ISP’s network and the customer’s equipment to support it end to end, and providers roll that out at very different speeds. Mobile carriers tend to lead, since replacing SIM-based infrastructure and phones happens faster than replacing millions of home routers. Some countries — India, several in Latin America — report majority IPv6 traffic through aggressive carrier rollouts, while others lag well behind because legacy fixed-line equipment simply was never upgraded. Countries that built out their internet infrastructure more recently, with less legacy IPv4-only equipment to depreciate, often leapfrog straight to IPv6-heavy networks, while countries sitting on decades of sunk investment in IPv4 gear upgrade far more cautiously.
Privacy differences
IPv6 usually gives each device its own public address instead of sharing one behind NAT, which sounds like it should be worse for privacy — but modern operating systems counter that with privacy extensions, generating a temporary, randomized IPv6 address per network and rotating it regularly instead of exposing a permanent hardware-derived one. IPv4 behind NAT hides individual devices from the outside by design, since a whole household shares one visible address; the trade-off is that CGNAT taken to an extreme mixes many unrelated households onto one shared address, which can cause its own problems, covered in our CGNAT guide. Older devices or networks that don’t enable privacy extensions by default expose a stable IPv6 address derived from hardware identifiers, which is easier to track over time than a shared, rotating IPv4 address behind NAT — one reason privacy extensions ship enabled by default in every mainstream operating system today.