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IPv4 vs IPv6: Why Both Still Exist

Published October 20, 2026 · Bipul Ranjan
networkingeducation

If you’ve ever checked your own IP address and seen two completely different-looking strings - something like 203.0.113.42 next to 2001:0db8:85a3::8a2e:0370:7334 - you’ve run into the fact that the internet currently runs two separate addressing systems at once, not one.

Why IPv4 ran out in the first place

IPv4 addresses are 32-bit numbers, which caps the total possible addresses at about 4.3 billion. That sounded like plenty in the 1980s. It isn’t anymore - there are more internet-connected devices than that today, and the pool of available IPv4 addresses has been effectively exhausted for years. IPv6 exists specifically to fix this: its addresses are 128-bit, which allows for more unique addresses than there are grains of sand on Earth, several times over.

So why hasn’t IPv4 just disappeared?

Because replacing a global addressing standard isn’t something that can happen overnight - or even over a decade, apparently. IPv4 and IPv6 aren’t directly interoperable; a device or network has to explicitly support IPv6 for it to work, and huge amounts of existing hardware, software, and internal business systems were built assuming IPv4 only. The practical solution has been dual-stack: most modern devices and networks run both protocols simultaneously, using IPv6 when it’s available end-to-end and falling back to IPv4 otherwise. This is why you’ll often see both addresses when checking your own connection - our What’s My IP tool shows both for exactly this reason.

What this means day to day

For most people, none of this requires any action - dual-stack support is handled automatically by your device and ISP. Where it does matter: if you’re running your own server or service, supporting both protocols matters for reachability, since some visitors will only have IPv6 connectivity (increasingly common on mobile networks) and others will only have IPv4. And if you’re troubleshooting a networking issue, it’s worth knowing which protocol is actually in play - a service that works over IPv4 but fails over IPv6 (or vice versa) is a real, if uncommon, category of bug.

If you’re working with IP ranges directly rather than just checking your own address, our Subnet / CIDR Calculator covers IPv4 CIDR notation specifically, and our DNS Lookup Tool shows both A (IPv4) and AAAA (IPv6) records for any domain side by side.