IPv6 Leaks Explained: A Blind Spot Many VPNs Still Have

What exactly is an IPv6 leak?

Every device connected to the internet needs an IP address — a numerical label that lets other computers know where to send data back to it. For most of the internet's history, that meant an IPv4 address, part of a addressing system designed decades ago with a fixed, and by now largely exhausted, pool of possible addresses. IPv6 is the newer addressing standard built to replace it, with a vastly larger address space, and it has been rolling out gradually across internet providers, mobile carriers, and operating systems for years now. The practical result is that a huge number of devices today are "dual-stacked" — they have both an IPv4 address and an IPv6 address active at the same time, and the operating system decides, connection by connection, which one to actually use.

A VPN's entire job is to intercept your device's outgoing traffic and route it through an encrypted tunnel to the VPN provider's server, rather than sending it out over your regular internet connection in the clear. Historically, a great deal of VPN tunneling software — protocol implementations, client apps, and the underlying network configuration they set up — was built with IPv4 as the assumed default, because for a long time that was simply what nearly all traffic was. An IPv6 leak is what happens when that assumption catches up with a device: the VPN tunnel correctly captures and encrypts your IPv4 traffic, but has no equivalent handling for IPv6, so any traffic your device happens to send over its IPv6 address goes out directly over your normal internet connection instead — completely bypassing the VPN, unencrypted, and visible to your ISP and to whichever site or service you're connecting to. This can happen while the VPN app itself shows no error, no warning, and a perfectly normal "connected" status, because from the app's point of view, it's doing its job on the IPv4 traffic it was built to watch.

The practical effect is a split connection that looks unified from the outside but isn't. Some of your traffic — potentially DNS lookups, some app connections, and depending on the situation, general browsing traffic to any IPv6-reachable website — goes out with your real, unmasked IPv6 address attached, revealing both your actual location-adjacent network identity and the destinations you're reaching, at the same time your VPN app is telling you everything is protected. That gap between what the app reports and what's actually happening on the wire is exactly what makes an IPv6 leak worth understanding on its own terms, rather than assuming it's just a subcategory of a DNS leak or a general connection failure.

Why does IPv4-focused VPN tunneling leave IPv6 exposed?

It helps to understand the mechanical reason this gap exists, because it isn't usually a case of a VPN provider not caring about IPv6 — more often it's a case of a tunnel being built, tested, and maintained around one addressing system while the other quietly rides along untouched.

When a VPN app connects, it typically does a specific, deliberate set of things to your device's network configuration: it creates a virtual network interface, adjusts your routing table so that IPv4 traffic gets sent through that virtual interface instead of your regular one, and often changes your DNS settings to point at the VPN's own DNS servers. All of that is real, meaningful work, and for IPv4 traffic it generally does exactly what it's supposed to. The problem is that a device's IPv6 configuration is a mostly separate set of settings, with its own routing table, its own address, and its own path onto the network — and unless the VPN app specifically reaches into that separate configuration and either tunnels it too or blocks it outright, IPv6 traffic keeps flowing exactly as it did before the VPN connected, using the same route it always used, straight out over your regular network connection.

A few specific technical patterns show up repeatedly behind this:

The VPN protocol or client software simply wasn't built to handle IPv6. Some VPN protocols and older client implementations were designed with IPv4 as the only target, and adding real IPv6 tunneling support requires deliberate engineering work that not every provider has prioritized equally. Where that work hasn't happened, IPv6 isn't leaking out of a bug so much as it's simply never been brought inside the tunnel in the first place.

The app tunnels IPv4 but doesn't block IPv6 as a fallback. Even providers that don't fully support tunneling IPv6 traffic can still close the gap by disabling IPv6 on the device's network adapter for the duration of the VPN connection, so there's no active IPv6 path left for traffic to leak through. Apps that skip this step leave IPv6 fully live and unprotected, sitting right alongside the protected IPv4 tunnel.

The operating system prefers IPv6 when both are available. Most modern operating systems are configured to prefer IPv6 over IPv4 whenever a destination is reachable over both, on the theory that IPv6 is the more modern, better-supported standard. That default preference works against an IPv4-only VPN tunnel: even though the VPN has created a protected IPv4 path, the OS will often try the unprotected IPv6 path first if it's available, specifically because it's designed to.

Mobile networks and newer ISP rollouts increasingly assign IPv6 by default. IPv6 adoption has grown substantially through mobile carrier networks in particular, along with a growing share of home ISPs, which means a device that had no active IPv6 connectivity a few years ago may well have it now, on a network or carrier plan the user never changed anything about. A VPN setup that was tested and seemed leak-free in the past can start leaking with no change on the user's end at all, simply because the network underneath it started offering IPv6 where it didn't before.

Manually configured VPN connections, rather than the provider's own app, skip IPv6 handling entirely. Setting up a VPN connection through an operating system's built-in client, or through a router's native VPN support, rather than through the provider's dedicated app, often means missing out on IPv6-specific protections the app would otherwise apply, since those protections are frequently implemented as app-level logic rather than something baked into the underlying protocol itself.

None of this requires bad faith on a provider's part. It's a genuinely awkward technical transition — the internet as a whole has been in a long, slow, multi-decade shift from IPv4 to IPv6, and VPN software, like a lot of other networking infrastructure, has had to catch up to a moving target rather than a fixed one. That said, the providers that have caught up matter considerably more in practice than the ones that haven't, which is exactly why checking for explicit IPv6 handling is worth doing rather than assuming any given VPN has it covered.

Why does an IPv6 leak actually matter?

It's worth being concrete about what an IPv6 leak exposes, because "leak" can sound abstract next to more familiar VPN vocabulary like encryption or server locations. In practice, a device sending traffic out over its real IPv6 address, unencrypted and outside the VPN tunnel, hands over two things at once: your device's actual network-assigned address, which can reveal your approximate location and your ISP, and — depending on what specifically leaks — the sites and services that traffic was headed to.

IPv6 addresses carry a particular wrinkle that makes this more sensitive than it might first appear: unlike the shared, frequently reassigned IPv4 addresses most home networks use, IPv6 addressing was designed with a far larger address space specifically so that individual devices can be assigned their own distinct, longer-lived address rather than sharing one behind a router's network address translation. That means an IPv6 leak can, in some configurations, be more directly traceable to a specific device over time than an equivalent IPv4 leak would be, rather than blending into the crowd of a shared, constantly-reassigned address pool.

The stakes vary by who's affected and why they're using a VPN:

For someone using a VPN mainly to unblock streaming content or add a layer of convenience on public Wi-Fi, an IPv6 leak is a genuine gap but a comparatively low-stakes one — it means part of the intended protection isn't actually working, without necessarily changing much day to day.

For anyone relying on a VPN specifically to keep their real location, ISP, or browsing destinations hidden — the kind of use case covered in our guide to VPNs for privacy — an IPv6 leak can quietly undo exactly the protection they thought they had. That's especially relevant for people in higher-stakes situations discussed elsewhere on this site, including journalists and human rights defenders, where a network-level leak isn't a minor inconvenience but a real exposure of who they're connecting to and from where.

An IPv6 leak also matters for a broader reason: it's one more concrete illustration that a "connected" indicator in a VPN app is a status report on what the app is aware of, not an independent guarantee that every category of traffic leaving the device is actually protected. IPv6 leaks, like DNS leaks, are a real-world example of that gap between reported status and actual network behavior, and they're specifically worth checking because the underlying cause — incomplete IPv4-only tunneling — is common enough across the VPN industry that it isn't a purely theoretical risk.

How is an IPv6 leak different from a DNS leak?

The two get mentioned in the same breath often, and they're related in the sense that both describe traffic slipping outside a VPN tunnel that's supposed to be catching everything, but they're distinct issues with somewhat different causes and somewhat different fixes. Our DNS leaks guide covers the DNS-specific case in detail; here's the short version of how they differ.

A DNS leak specifically concerns the lookup requests your device sends to translate a domain name into an IP address — it's a leak of what you're looking up, not necessarily your own identifying address. A DNS leak can happen over IPv4 alone, with no IPv6 involvement at all, if the VPN simply fails to redirect DNS queries to its own servers.

An IPv6 leak is broader: it's about an entire addressing system, and an entire category of traffic, bypassing the tunnel — not just DNS lookups, but potentially general browsing traffic, app connections, and yes, DNS queries too, if your operating system happens to resolve them over IPv6. In fact, one of the more common and more serious forms of DNS leak is specifically an IPv6 DNS leak — DNS queries going out over an untunneled IPv6 path even while IPv4 DNS is correctly protected. So the two overlap at that intersection, but IPv6 leaks aren't limited to DNS the way DNS leaks are limited to lookup traffic.

Practically, this means the two require somewhat different testing: a DNS leak test alone may not surface a general IPv6 leak if your DNS queries happen to route correctly over IPv4 while other IPv6 traffic doesn't. A dedicated IPv6 leak VPN test, covered below, checks specifically for exposed IPv6 connectivity rather than DNS resolution alone, and running both kinds of checks gives a more complete picture than either alone.

What causes IPv6 leaks in practice, beyond the basic mechanics?

Beyond the underlying technical explanation, a few everyday situations come up repeatedly as the actual moments an IPv6 leak tends to surface.

Connecting from a network that only recently started offering IPv6. Because IPv6 rollout has been gradual and uneven across ISPs and regions, a network that had no IPv6 connectivity when you first tested your VPN setup can start offering it later without any obvious announcement, silently reactivating a leak path that genuinely wasn't there before.

Switching to a mobile carrier or a new SIM. Mobile networks have generally moved faster on IPv6 adoption than many fixed-line ISPs, so a VPN setup that tested clean on a home Wi-Fi network can behave differently on a mobile data connection, particularly if the VPN app's IPv6 handling differs between its desktop and mobile versions.

Using a router-level VPN configuration. Setting up a VPN directly on a home router, so every connected device is covered without installing an app on each one — a setup discussed in our guide to protecting a whole household with a VPN — adds an extra layer where the router's own IPv6 handling has to be configured correctly, separately from whatever the VPN provider's official app would normally handle on a single device.

Using a manually configured protocol connection rather than the provider's app. As mentioned earlier, IPv6 blocking or tunneling is often implemented as an app-level feature, not something inherent to the underlying VPN protocol. A user who configures a VPN connection directly through their operating system's native client, bypassing the provider's own app entirely, may lose that protection without realizing it, since the app-level safeguard simply never gets applied.

Operating system or firmware updates that re-enable IPv6. If IPv6 was previously disabled at the device level as a workaround, an operating system update or a router firmware update can sometimes reset that setting back to its default, quietly reactivating IPv6 connectivity — and the associated leak risk — without the user changing anything intentionally.

Split tunneling configurations. VPN apps that offer split tunneling, letting you choose which apps or traffic go through the VPN and which don't, can sometimes handle IPv6 inconsistently within that split — an app that's meant to have its IPv4 traffic tunneled may still leak that same app's IPv6 traffic outside the tunnel if the split tunneling feature only accounts for IPv4 routing rules.

How do you run an IPv6 leak VPN test?

Checking for an IPv6 leak doesn't require special tools or technical expertise, and like a DNS leak test, it takes a couple of minutes with just a browser and your VPN app.

1. Check your IPv6 status before connecting to the VPN, as a baseline. Visit an IP-checking site that reports IPv6 status specifically before turning your VPN on. If the site shows a real IPv6 address, that confirms your device and network do have active IPv6 connectivity — which means there's a real leak path for your VPN to either close or leave open. If no IPv6 address shows up at all, even without a VPN running, your specific network or device may not have IPv6 active, which changes how relevant this particular check is for your setup.
2. Connect to your VPN normally. Choose the server or location you'd typically use, and wait until the app clearly shows a connected state before testing — the same caution that applies to DNS leak testing applies here, since testing mid-connection or during a reconnect can produce misleading results.
3. Revisit an IP-checking or leak-testing site that explicitly reports IPv6. Not every IP-checking tool checks IPv6 separately from IPv4, so it's worth using one that clearly labels both — plenty of free, independent testing sites do this, generally showing an IPv4 result and an IPv6 result side by side, sometimes as part of the same combined tool used for DNS leak testing.
4. Compare the IPv6 result against your pre-VPN baseline and your VPN's expected behavior. The next section walks through how to read this, but broadly: no IPv6 address detected, or an IPv6 address that clearly belongs to your VPN provider, is the result you want. Your own real IPv6 address showing up while the VPN is connected is a leak.
5. Repeat the test after switching servers, apps, networks, or devices. Just like DNS leak results, an IPv6 leak VPN test result on one network, one server, or one device doesn't automatically apply to every other combination. Re-testing after any meaningful change — new server location, new network, a VPN app update — is the more reliable habit.

Some VPN providers also include an IPv6 status check directly inside their own app or on their support site, alongside or as part of a broader connection or DNS leak test — worth looking for specifically if your provider offers one, since it's testing the exact configuration the provider intends to ship rather than a generic third-party check.

How do you interpret the results of an IPv6 leak test?

The result of an IPv6 leak test is generally one of a few possible outcomes, and each one means something slightly different.

No IPv6 address detected at all. This is a clean result in the sense that means nothing leaked, but it can mean two different things underneath: either the VPN is actively and correctly blocking IPv6 while connected, which is exactly what you want, or your device or network simply doesn't have IPv6 connectivity in the first place, in which case the VPN isn't really being tested on this front at all. Comparing against your pre-VPN baseline check from the previous section is what tells these two cases apart — if you had a real IPv6 address before connecting and none while connected, that's the VPN actively closing the gap.

An IPv6 address that matches your VPN provider. Some VPN providers now genuinely tunnel IPv6 traffic through the encrypted connection rather than simply blocking it, in which case a leak test may show an IPv6 address, but one that belongs to the VPN's own infrastructure rather than your ISP. This is also a good result — it means IPv6 traffic is protected, just via tunneling rather than blocking.

Your own real IPv6 address. This is the leak. It means your device's actual, ISP-assigned IPv6 address is visible to the site you're testing from, and by extension to any other site or service your device connects to over IPv6 while the VPN is active — regardless of what the VPN app's connection status shows.

Inconsistent results between repeated tests. Similar to intermittent DNS leaks, an IPv6 leak that shows up on some tests and not others can point to a race condition between the VPN's connection process and the device's network stack, or to an operating system preferring IPv6 only under specific conditions. Treat an intermittent result as a real leak worth investigating rather than a fluke, since the underlying exposure is still there even if it doesn't trigger on every single test.

One thing worth flagging directly, because it trips people up: a clean IPv4 result — a VPN server's IP address showing up correctly when you check your general "what's my IP" status — says nothing on its own about IPv6. It's entirely possible, and common, to have a VPN that correctly masks your IPv4 address while leaving IPv6 completely exposed, because most general-purpose "what's my IP" checks default to showing whichever address type the connection actually used, which may not be IPv6 depending on the site being checked. That's exactly why a dedicated IPv6 leak VPN test, using a tool that explicitly reports both address types, matters — a normal-looking IP check by itself isn't sufficient to rule this out.

How do you fix or prevent an IPv6 leak?

The right approach depends somewhat on what caused it, but a handful of general fixes cover most real situations.

Choose a VPN provider that explicitly documents IPv6 handling

The most durable fix is starting with a provider that has actually built and documented IPv6 protection, whether that means genuinely tunneling IPv6 traffic or reliably blocking it for the duration of the connection. This is a reasonable, specific question to check for when comparing providers, alongside things like logging policy and protocol support — our individual reviews, including our NordVPN review and Proton VPN review, are a starting point for looking at how a given provider documents its own approach to this.

Disable IPv6 at the device or router level, if your VPN doesn't handle it

If a leak test shows your real IPv6 address and your VPN provider doesn't offer explicit IPv6 tunneling or blocking, disabling IPv6 directly on your device — or, for broader coverage, at your router — removes the untunneled path entirely, since there's no active IPv6 connectivity left for traffic to leak through. This is a device or network-level networking setting rather than something the VPN app itself controls, so the exact steps differ by operating system and router model, but it's a widely documented and reversible change.

Look for an explicit "block IPv6" or "IPv6 leak protection" setting in your VPN app

A number of VPN apps expose this as a specific, named toggle in their settings, similar to a DNS leak protection setting, rather than assuming it's always silently applied. If your app has a setting along these lines, confirming it's switched on is a quick, concrete step, and it's worth re-running a leak test afterward to confirm the setting is actually doing what its name implies.

Use the provider's official app rather than a manual protocol configuration

Since IPv6 handling is frequently implemented as app-level logic, using the VPN provider's own official app — rather than manually configuring the underlying protocol through your operating system's built-in VPN client — is more likely to include whatever IPv6 protection the provider has built, if any. A manual configuration can technically establish a working VPN tunnel while skipping this kind of protection entirely.

Pair IPv6 leak protection with a kill switch, not as a substitute for it

A kill switch blocks all internet traffic if the VPN connection drops, which addresses a different risk — sudden exposure after a disconnect — rather than the ongoing, parallel exposure an IPv6 leak represents while the VPN is actively connected. The two protect against different failure modes and are worth having together rather than assuming one covers the other.

Re-test after any change to your network, device, or app version

Because IPv6 rollout by ISPs and mobile carriers is uneven and ongoing, and because operating system or firmware updates can silently reset a previously disabled IPv6 setting back to default, a single clean IPv6 leak test result isn't a permanent guarantee. Treating it as valid for the specific network, device, and app version you tested, and re-checking after any meaningful change, is a more realistic habit than testing once and assuming it holds indefinitely.

Do all VPNs handle IPv6 leaks by default?

No, and this is genuinely one of the more inconsistent areas across the VPN industry, more so in some ways than DNS leak protection, which has become a fairly standard baseline feature among established providers. IPv6 handling still varies meaningfully — some providers tunnel IPv6 traffic properly, some block it outright as a simpler and still effective safeguard, and some apps, particularly older ones or ones that haven't been updated to keep pace with IPv6's growing prevalence, do neither, leaving the gap wide open without any indication to the user.

Platform matters here too. A VPN provider's IPv6 handling isn't necessarily uniform across every version of its app — a well-protected desktop app doesn't guarantee the same provider's mobile app, browser extension, or router-level setup handles IPv6 identically. If IPv6 leak protection specifically matters to how you use a VPN, it's worth testing on the actual platform and app version you use most, rather than assuming a good result on one device transfers to another.

Free or lower-resourced VPN services deserve particular scrutiny here as well, for similar reasons to DNS leak protection: building and maintaining reliable IPv6 handling, across every operating system and network scenario, is ongoing engineering work, and a service with fewer resources is statistically less likely to have prioritized it to the same degree as a larger, more established provider — not necessarily out of neglect, but because it's one of several competing priorities for a smaller engineering team. Testing your own specific setup remains the only way to know for certain, regardless of provider size or reputation.

Which platforms and devices are most affected by IPv6 leaks?

IPv6 leak risk isn't evenly distributed across every kind of device and connection — some setups are more exposed than others.

Mobile devices on cellular data. Mobile carriers have generally moved faster on IPv6 rollout than many fixed-line ISPs, which means a phone on cellular data is statistically more likely to have active IPv6 connectivity than the same phone on an older home Wi-Fi network — and mobile VPN apps don't always receive the same level of IPv6-specific engineering attention as their desktop counterparts from the same provider.

Newer home networks and newer ISP equipment. ISPs have been rolling out IPv6 gradually, often tied to newer router or modem hardware, so a household that recently upgraded its internet equipment may have gained IPv6 connectivity it didn't previously have, changing the leak picture for every device on that network at once.

Router-level and whole-home VPN setups. As mentioned earlier, configuring a VPN directly at the router adds a layer where the router's own IPv6 handling has to be correctly configured, separately from any protection the provider's device-level app would normally apply — worth checking specifically if your household relies on this kind of setup, discussed in our guide to VPNs for families and shared households.

Manually configured connections on any platform. Regardless of device type, a VPN connection set up manually through an operating system's built-in client, rather than through the provider's dedicated app, is consistently a higher-risk configuration for IPv6 leaks, since app-level IPv6 protections are typically skipped entirely in that setup.

Older or infrequently updated VPN app installations. IPv6 handling has generally improved across the industry over time as awareness of the issue has grown, which means an outdated version of an otherwise capable VPN app may be missing IPv6 protections that the same provider has since added in newer releases.

Does finding an IPv6 leak mean my VPN provider is untrustworthy?

Not automatically, and it's worth applying the same caution here as with a DNS leak: a single leaked test result is more often a sign of an unaddressed technical gap than evidence of bad faith. Given how unevenly IPv6 support has been built out across the VPN industry, and how gradually IPv6 itself has rolled out across networks and carriers, a provider whose IPv6 handling hasn't caught up isn't necessarily the same as a provider that's being deliberately careless with your traffic.

That said, a confirmed leak is still worth acting on regardless of the underlying cause — the practical exposure is the same either way. If your provider has no documented IPv6 handling at all, disabling IPv6 at the device level, as covered earlier, is a reasonable and immediate workaround while you decide whether to raise it with the provider directly or consider a different one. A provider that, once informed, has no plan to address IPv6 handling, or whose app continues to leak IPv6 traffic across repeated updates, is a more legitimate reason for longer-term concern than a single isolated test result.

How often should you test for IPv6 leaks?

There's no universal schedule, since how much this matters depends on your own situation and how much you're relying on the VPN for genuine privacy versus convenience. A reasonable baseline approach: test once when you first set up a new VPN app or a new device, again after any major app or operating system update, and again any time you connect from a network you haven't used before — a new home ISP connection, a new mobile carrier or SIM, a hotel or workplace network. Because IPv6 availability itself can change on a network you already use, without you doing anything differently, an occasional spot-check even on familiar networks is a reasonable habit rather than unnecessary caution.

If you're in a higher-stakes situation — protecting sensitive reporting or communications, operating in a hostile network environment, or any context where a leaked real IP address carries genuine personal risk — testing more deliberately, and specifically before sessions where it matters most, is worth the small amount of extra time. In that context, an IPv6 leak VPN test takes far less time than the exposure it's meant to catch would cost.

Practical takeaway

An IPv6 leak is a specific, common, and often invisible gap: a VPN tunnel built mainly around IPv4 traffic can leave IPv6 traffic — including, in some cases, DNS lookups and general browsing connections — flowing outside the encrypted tunnel entirely, exposing your real IPv6 address and the destinations you're reaching, all while the VPN app shows a normal connected state. It happens because much of the VPN industry built its tunneling infrastructure before IPv6 was as widespread as it is now, and not every provider or app version has fully closed that gap since. It's checkable in a couple of minutes with a free IPv6 leak VPN test that reports IPv6 status specifically, comparing what shows up while connected against your own real address. A clean result means either your VPN is actively tunneling or blocking IPv6 correctly, or your device simply doesn't have active IPv6 connectivity to leak in the first place — worth confirming which one it is. Treat any result as specific to the network, device, and app version you tested, rather than a permanent guarantee, and re-test after any meaningful change. Choosing a provider that explicitly documents its IPv6 handling, or disabling IPv6 at the device level if it doesn't, covers the practical side of this for nearly everyone.