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IPv4 vs IPv6: what's the difference, and which are you using?
IPv4 is the internet's original 32-bit addressing scheme — about 4.3 billion addresses, exhausted years ago — and IPv6 is its 128-bit replacement with effectively unlimited space; most connections today quietly use both, and you can find out which in ten seconds with two curl flags. The practical differences for you are narrower than the protocol wars suggest: address sharing, reachability, and one genuine privacy trap for VPN users. This guide covers exactly those.
Maintained by the ipconfig.io team · Reviewed 1 July 2026
Which one am I using right now?
ipconfig.io answers over both protocols, so you can test each family directly:
bash
curl -4 ipconfig.io # force IPv4 → 203.0.113.42
curl -6 ipconfig.io # force IPv6 → 2001:db8:85a3::8a2e:370:7334Three outcomes:
- Both return addresses — you're dual-stack. Each connection picks a family (modern systems race both and usually land on IPv6). This is the common, healthy state.
-6fails to connect — your network is IPv4-only. Still true for many ISPs; nothing is broken.-4fails — rare (IPv6-only with translation for v4 sites, mostly mobile carriers).
Note that the two addresses are different identities: a site you visit sees one or the other per connection, and the full lookup — location, ASN, reverse DNS — is computed for whichever family carried that request.
What's actually different
| IPv4 | IPv6 | |
|---|---|---|
| Address size | 32-bit — 203.0.113.42 | 128-bit — 2001:db8::1 |
| Address space | ~4.3 billion (exhausted) | ~3.4×10³⁸ (effectively unlimited) |
| Who shares addresses | NAT everywhere; CGNAT at many ISPs | Every device can have a globally unique address |
| Typical assignment | One public IP per household (or shared) | A whole prefix (billions of addresses) per household |
| Reachability | Inbound requires port forwarding; impossible behind CGNAT | Direct addressing possible (firewalls still apply) |
The scarcity story explains most of what you experience day to day. IPv4 ran out, so ISPs layered address sharing on top — first home NAT, then carrier-grade NAT — which is why inbound connections, self-hosting and even geolocation accuracy get messy on IPv4. IPv6 removes the scarcity, so none of the sharing machinery is needed.
A common privacy worry, answered: IPv6 addresses don't broadcast your identity any more than IPv4 does — and modern systems use privacy extensions (temporary, rotating addresses) by default, so your device isn't advertising one fixed address to every site either. What an IP does reveal is the same for both families.
Is IPv6 faster?
Sometimes, barely. Skipping NAT translation and occasionally cleaner routing can shave a little latency; congested or poorly-peered IPv6 paths can add some. Measurements across large networks show single-digit-percent differences in both directions. It is not a lever worth pulling for speed.
Should I disable IPv6?
The advice "just disable IPv6" mostly dates from a decade ago. Today: leave it on. It's actively maintained, your OS prefers it deliberately, and disabling it can slow name resolution and break peer-to-peer apps.
The one scenario with a real problem is a VPN that only tunnels IPv4 on a dual-stack connection: your IPv4 traffic hides in the tunnel while IPv6 traffic — carrying your real, un-VPN'd address — walks straight past it. That's not an IPv6 flaw; it's a VPN gap. The VPN leak guide shows how to test both families in two commands, and the durable fix is a VPN that tunnels or blocks IPv6 rather than disabling the protocol system-wide.
Frequently asked questions
What's the difference between IPv4 and IPv6? 32-bit vs 128-bit addressing: IPv4 is exhausted and papered over with NAT and sharing; IPv6 has effectively unlimited space and gives devices globally unique addresses.
How do I know which I'm using?curl -4 ipconfig.io and curl -6 ipconfig.io — both answering means dual-stack; a -6 connection failure means IPv4-only.
Is IPv6 faster? Occasionally and marginally, in both directions. Don't choose on speed.
Should I disable IPv6? No — except as a stopgap when your VPN doesn't tunnel it, and the better fix is a VPN that does.
Next steps
- Check if your VPN is leaking your real IP — the dual-stack test every VPN user should run once.
- What is CGNAT? — the IPv4-scarcity workaround you're probably behind.
- Find your public IP from the terminal — more one-liners built on the same endpoints.