> For the complete documentation index, see [llms.txt](https://docs.ipcheck.ing/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.ipcheck.ing/knowledge-base/concepts/ipv4-vs-ipv6.md). # IPv4 vs IPv6 Why does your connection sometimes show one address, and sometimes two that look nothing alike? Because there are two versions of the internet protocol running side by side, and most modern connections speak both. ## An IP address is a postal address Every device that talks to the internet needs an address, so replies know where to come back to. That is all an IP address is: a destination label attached to each piece of data. There are two formats in use today. **IPv4** looks like this: ``` 203.0.113.42 ``` Four numbers, each from 0 to 255, separated by dots. **IPv6** looks like this: ``` 2001:0db8:85a3:0000:0000:8a2e:0370:7334 ``` Eight groups of hexadecimal digits, separated by colons. It is usually written in a shortened form, where a long run of zeros collapses into `::`: ``` 2001:db8:85a3::8a2e:370:7334 ``` Both do the same job. IPv6 is simply the newer format, with a far larger supply of addresses. ## Why IPv6 exists: the addresses ran out IPv4 was standardised in the early 1980s. Its address format allows about 4.3 billion unique addresses. At the time that seemed generous. It was not. Today there are far more connected devices than people: phones, laptops, televisions, routers, cameras, servers. The regional organisations that hand out IPv4 addresses reached the bottom of their free pools during the 2010s. New IPv4 addresses are now mostly obtained by transfer or lease from someone who already holds them, and they cost real money. IPv6 was designed to end that problem permanently. Its address space is not slightly bigger — it is roughly 340 undecillion addresses, a number with 39 digits. There is no realistic scenario in which it runs out. ## Side by side | | IPv4 | IPv6 | | --------------- | --------------------- | ----------------------------- | | Example | `203.0.113.42` | `2001:db8::1` | | Address size | 32 bits | 128 bits | | Total addresses | \~4.3 billion | \~340 undecillion | | Standardised | 1981 | late 1990s | | Address sharing | Very common | Usually unnecessary | | Written with | Dots | Colons | | Support today | Essentially universal | Widespread, but not universal | ## Dual stack: why you often have both You might expect a switch-over date, where everyone moves from IPv4 to IPv6 on the same day. That never happened, and it never could. The two formats are not compatible with each other. An IPv4-only device cannot talk directly to an IPv6-only device. So the industry chose a different path: run both at once. This is called **dual stack**. Your device gets an IPv4 address *and* an IPv6 address, and uses whichever one works for the site it is trying to reach. That is why a tool like MyIP may show you two completely different addresses at the same time. They are not a contradiction. They are two doors into the same house. When your browser has both options, it typically tries both and uses whichever answers first, with a mild preference for IPv6. This behaviour has a name — Happy Eyeballs — and it is one reason the address a website sees can differ between visits. ## Why a site might see one and not the other * **The site has no IPv6 address.** Many websites still publish only an IPv4 address. Your browser has no choice: it uses IPv4. * **Your network has no IPv6.** Some home and mobile networks are still IPv4-only. Some office networks disable IPv6 deliberately. * **A VPN or proxy handles only one of them.** This is a common surprise. If your VPN carries IPv4 traffic but leaves IPv6 alone, an IPv6-capable site can see your real address while IPv4 sites see the VPN. See [Am I Leaking My Real IP?](/knowledge-base/diagnose/am-i-leaking-my-real-ip.md). * **Your IPv6 address changes more often.** Many devices rotate their outgoing IPv6 address regularly as a privacy measure, so today's IPv6 may not be tomorrow's. ## Why it matters to you * **Your IPv4 address is probably shared.** Because IPv4 is scarce, your provider likely places many customers behind one public address. Your IPv6 address, if you have one, is much more likely to be yours alone. See [Public, Private & CGNAT Addresses](/knowledge-base/concepts/public-private-cgnat.md). * **Two addresses means two chances to leak.** A privacy setup that only covers IPv4 is only half a setup. * **Location data can differ between them.** Geolocation databases often know an IPv4 range better than the matching IPv6 range, so the two can report different cities. See [GeoIP: How IP Geolocation Works](/knowledge-base/concepts/geoip-explained.md). ## Common misconceptions **"IPv6 is faster."** Not by itself. On some paths it is slightly faster because it avoids address translation; on others it is slower because the IPv6 route is less optimised. Speed is dominated by distance and routing, not by protocol version. **"IPv6 is more private."** Not automatically. An IPv6 address that never changes is easier to track than a shared IPv4 address. Modern operating systems counter this with rotating temporary addresses, but the result depends on your settings. **"I should turn IPv6 off."** Usually a bad idea. Disabling it can make some sites slower or unreachable. If IPv6 is causing a problem, the fix is normally in your VPN or router configuration, not in switching the protocol off. **"IPv4 is being shut down."** There is no shutdown date. IPv4 will stay in service for a very long time. IPv6 adoption has grown steadily and now carries a large share of global traffic, but it varies enormously by country and by network — some countries are majority IPv6, others barely use it at all. {% hint style="info" %} **See it yourself on MyIP** The **IP Infos** section shows your IPv4 and IPv6 addresses on separate cards, each queried from several sources. If one card comes back empty, your connection only has that one protocol. Prefer the terminal? The [Curl API](/knowledge-base/getting-started/curl-api.md) offers three endpoints: one that answers over IPv4 only, one that answers over IPv6 only, and one that answers over whichever your machine prefers. Comparing all three tells you exactly which protocol your system reaches for first. {% endhint %} ## Related concepts * [Public, Private & CGNAT Addresses](/knowledge-base/concepts/public-private-cgnat.md) — why your IPv4 address is probably shared * [What Is an ASN?](/knowledge-base/concepts/what-is-an-asn.md) — the networks that carry both protocols * [GeoIP: How IP Geolocation Works](/knowledge-base/concepts/geoip-explained.md) — why the two addresses can report different locations * [Reading Your IP Cards](/knowledge-base/getting-started/reading-your-ip-cards.md) — what each field on the cards means --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. 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