Torrent IP Leak Test: Why Your Client Shows a Different IP Than Your Browser

A VPN can show "Connected" while your torrent client announces a completely different IP address to the tracker than the one your browser shows. A browser leak check never catches that, because it does not ask your client anything. A torrent IP leak is therefore its own problem, with its own cause and its own fix.

There are six things worth checking, and they fail independently. Your browser address can be hidden while your client announces your real one. Your DNS can be clean while your browser hands out your address over WebRTC. Each needs its own test and has its own fix.

This guide explains what causes a torrent IP leak, what the BitTorrent specification says about it, and the one client setting that fixes it. It then covers the five checks that run on the machine itself, how to read a result that only looks like an IP leak, and what to change when one genuinely fails. Every figure carries its source and its date, including one correction to an earlier version of this page.

Author: David Miller Senior Privacy & VPN Architect

This page used to open with a statistic about how many users are leaking. I have removed it, along with two similar claims, because I could not produce a source for any of them. What replaced them is a peer-reviewed study that measured the thing they were guessing at, and it is named and dated below so you can read it yourself rather than take my word for it.

My limits, plainly. Every mechanism here that I could source to a standard or to a vendor's own documentation is quoted and named; the rest is reasoning, and the text says which is which. I have not audited the VPN industry and I will not tell you which provider is best, because leak behavior changes with every software update and the answer that stays true is the one you get from testing your own setup.

What a VPN Leak Actually Is

A VPN leak is traffic that leaves your device outside the encrypted tunnel while the tunnel is up. The client is not lying when it says "Connected" — the tunnel genuinely exists. Something is simply going around it, and a torrent client is one candidate, because it chooses its own network interface.

A VPN is not the only thing deciding where your traffic goes. Your operating system has its own resolver, your browser has its own networking stack, your torrent client binds to its own interface, and your network may offer a protocol the VPN never claimed to carry. Any of those routes around the tunnel with no error anywhere.

This is not a rare or exotic failure. The VPN analysis published in Proceedings on Privacy Enhancing Technologies examined commercial clients directly. It reported: "We analyse 14 of the most popular ones, inspecting their internals and their infrastructures. Despite being a known issue, our experimental study reveals that the majority of VPN services suffer from IPv6 traffic leakage."

That paper is Perta, Barbera, Tyson, Haddadi and Mei, volume 2015 issue 1, pages 77 to 91. Its age cuts both ways: the products have changed, and its own phrase "Despite being a known issue" tells you the problem was already old in 2015. It establishes a structural weakness, not a rumor.

So the question is not whether leaks happen but which of them your setup has, and that takes about five minutes. If the VPN client itself is the weak part, this site does keep a ranking of VPNs on privacy grounds. Read it as a shortlist to test rather than a verdict, for the reason section ten gives: no ranking survives the next client release.

Why a Torrent IP Leak Happens When Your Browser Looks Clean

Your browser and your torrent client are two different programs opening two different connections. A browser leak test asks your browser; it cannot ask your client, and the client is the program announcing your address to strangers. So the two can disagree, and on a misconfigured setup they do.

A separate test exists because of how a tracker works. ipleak.net, which named the feature "Torrent Address detection", publishes the method plainly: "To detect data from your torrent client we provide a magnet link to a fake file. The magnet contains an http url of a controlled by us tracker which archives the information coming from the torrent client."

You add the magnet, your client announces itself, and the tracker writes down the address the announcement came from. Two things could undermine that, and the specification is honest about both. The UDP tracker protocol carries a field where a client can state its own address, but it defaults to zero, and BEP 15 notes that "most trackers will only honor the IP address field under limited circumstances".

The second is spoofing, and the same document says outright that "it is possible to spoof the source address of a UDP packet". Its answer is a handshake: the tracker issues a connection_id first, and "If the client spoofed it's source address, it won't receive this value". The tests worth using sidestep the question anyway, because ipleak's magnet points at an HTTP tracker, so the address is established by a TCP connection rather than by a single datagram.

The mechanism underneath is one sentence in the IPv6 tracker extension. BEP 7 states that "Each announce should use the corresponding local IP address as the source address of the connection", and that "The source address is set on a socket using the bind() call, before connecting". A torrent client binds to a local interface. Bound to your ordinary adapter instead of the VPN's, it announces your real address while the browser stays correctly tunneled.

So a torrent IP check runs like this: connect the VPN, add the magnet link the test gives you, let the client announce, and read the address reported back. A pass shows the VPN's address, a fail shows yours, and the fix is a client setting rather than a VPN one. In qBittorrent it is the network interface option, on the Advanced tab rather than Connection, and it ships set to any interface — the default that permits a leak rather than one that causes it.

That test now lives on this site. Run the torrent IP leak test with your VPN connected and note the address it reports back, because that is the number every check below is compared against. Then work through the five that follow, because a passing torrent test tells you nothing about your DNS.

What Each Leak Exposes, and Who Sees It

These are not degrees of the same problem. They are separate mechanisms with separate causes: a torrent leak and a DNS leak have nothing in common but the word, and a setup can pass every one of them and still fail the last. Read the table as a checklist rather than a ranking.

The word doing the damage is "Connected". A VPN connected and still leaking looks identical, from the client's side, to a VPN connected and watertight. There is no warning state between the two. That is the whole reason the only trustworthy signal comes from outside the software.

The last is the only one with a time limit, and that makes it the easiest to underestimate. Whatever you were transferring during the gap went out under your real address, and there is no taking it back.

How to Check if Your IP Is Leaking Past the VPN: The Browser Address Test

Start the browser side here, because until this one passes nothing further is worth testing. Note your real details before connecting, then compare after.

Before connecting, record four things about your public IP: the address itself, the city, the country, and the provider name shown. Then connect, reload, and check all four changed. A matching country with the wrong city is usually a geolocation database being imprecise rather than a leak. The provider name is the more reliable field to watch.

If any of your real details survive the connection, stop. The cause is usually a client that failed to establish rather than a subtle leak, and no amount of DNS or WebRTC checking will tell you anything useful until that is fixed.

The DNS Leak Test

This leak has the worst ratio of damage to visibility: your address can be hidden while every site name you request goes to your provider's resolver in plain view.

Before your browser can reach a site it has to turn the name into an address, and that request goes to whichever DNS resolver your system is configured to use. A VPN is supposed to replace that resolver with its own. When it does not, the tunnel carries your traffic while your provider keeps a list of everywhere you went.

To test it, connect and then query a name directly and look at which server answers. Every resolver that appears should belong to the VPN, not to your provider and not to your router. If your client has a setting called DNS leak protection, switch it on before you test, so that you are testing the configuration you actually intend to use.

That part has to happen on your own machine, with your system's own resolver query. A public lookup tool reads a domain's records and its authoritative nameservers, which is a different job and will not tell you which resolver your system picked.

Two results are worth telling apart. Your provider's name in the resolver list is a leak; a resolver in the right country with a name you do not recognize is usually the VPN's own infrastructure, which is a pass.

One Windows behavior is worth knowing by name: smart multi-homed name resolution. Microsoft describes it as issuing "parallel DNS, link local multicast name resolution (LLMNR) and NetBIOS over TCP/IP (NetBT) queries across all networks", and adds that "In the event that multiple positive responses are received, the network binding order is used to determine which response to accept". With a VPN up, one of those networks is your ordinary connection.

The part worth getting right is the fix, because the obvious one does not do what its name suggests. Microsoft's own policy text says that enabling "Turn off smart multi-homed name resolution" means "the DNS client won't perform any optimizations. DNS queries will be issued across all networks first." Turning the feature off therefore still sends DNS out every network.

If the queries go out regardless, the only thing that makes them safe is every active adapter having a resolver you trust, which is what a VPN client's own DNS handling is for when it works.

The WebRTC Leak Test

WebRTC is the browser feature behind video calls and peer-to-peer connections in a page. To make a direct connection work it has to find out what address you can be reached on, and it has a standard way of asking.

A browser uses STUN, which Mozilla's introduction to WebRTC protocols defines as "a protocol to discover your public address and determine any restrictions in your router that would prevent a direct connection with a peer". The same page describes the exchange: "The client will send a request to a STUN server on the Internet who will reply with the client's public address and whether or not the client is accessible behind the router's NAT."

Read that with a VPN in mind. The browser is asking a third party what address it appears to have, in order to tell a peer. Whether the answer is the VPN's address or your real one depends on how the browser's networking is routed, which a VPN client influences only if it routes or blocks all UDP itself.

The test takes seconds: connect, load a page that reads the addresses your browser will offer, and compare them against the VPN address from the address check. A pass shows only the VPN address. A fail shows your real one alongside or instead of it, and that is a browser leak rather than a tunnel failure. The WebRTC test and its browser fixes, step by step goes further into this one than a single section can.

On fixing it, one caution. Disabling WebRTC in the browser works, and so does a dedicated extension, but a browser carrying an unusual set of extensions is itself easier to recognize across sites. If you want to be less identifiable rather than only less locatable, weigh that before installing three of them.

The IPv6 Leak Test

This is the leak the study above measured, and its cause is structural. Many VPNs were built to carry IPv4 and to deal with IPv6 by pretending it is not there.

If your provider gives you both an IPv4 and an IPv6 address, and the site you visit supports IPv6, your connection may prefer IPv6. It then goes straight out with your real address attached. Your IPv4 traffic is still tunneled correctly the whole time, which is exactly why nothing looks wrong.

Testing it is a two-step comparison. Disconnect and check whether you have an IPv6 address at all; if you do not, this leak cannot affect you. If you do, connect and check again. A pass is either no IPv6 address, meaning the VPN blocks it, or one belonging to the VPN.

Both are legitimate designs and they are not equivalent. Blocking costs you IPv6 connectivity while the VPN runs; routing keeps it and is more work to build. Mullvad documented adding it as far back as September 2014, in a post announcing IPv6 support: "Now it can route all IPv6 traffic through the VPN server." The same post tells you to switch the setting on yourself, so it is not a capability you can assume you have.

If your VPN neither blocks nor routes IPv6, turning IPv6 off on the device forces everything back through IPv4, which the tunnel does handle. It is a blunt fix and it works. How the two protocols differ at the packet level covers what actually changed between them.

Testing the Kill Switch

A kill switch blocks your traffic when the tunnel drops, so a momentary failure is not an exposure. It is the one protection whose failure you never notice until afterwards.

Test it by causing the drop yourself. Confirm the setting is on, note the VPN address, then break the connection deliberately by switching servers or turning the network off for a moment. Do not simply quit the client: a clean exit is not a dropped tunnel, and a switch that releases its rules on shutdown will look like a failure when it is not. Immediately try to load anything.

A working kill switch means nothing loads, which is the correct and slightly alarming result. If pages keep loading during the gap the switch is not doing its job, and everything you were transferring went out under your real address.

Worth knowing before you test: some kill switches block the whole device and others block only chosen applications. The second kind will let a browser through while blocking what you actually configured. How a kill switch decides what to cut off covers the difference between those two designs.

The Complete Checklist

Run them in this order, because each rules out a reason the next might give a confusing answer. The torrent test goes first because it is the only one that tests a different program. The whole sequence takes about five minutes once you have done it.

The order also buys you a clean read on the kill switch. Test the switch first, before you know the tunnel is sound, and a failure tells you nothing: the traffic that got through may have been leaking anyway. Test it last and a failure means one thing.

One addition for anyone seeding as well as downloading. A client left running after you close the VPN keeps announcing. Bound to the VPN's interface it stops listening instead, which is the safe failure; unbound, it announces from whatever interface remains. Either way, stop the client before the tunnel rather than after it.

How to Fix Each Leak

Most fixes are a setting rather than a rebuild. The table below puts the thing most likely to work first for each leak. The last column is the honest signal that the client itself is the problem and no setting will save it.

On choosing a provider, this page does not rank them. Leak behavior changes with every client release, so any table of recommendations is stale the day it publishes, and a service called safe because someone tested it once is worth less than a test you ran this morning.

What holds up is narrower. A client that documents how it handles IPv6, offers a system-level kill switch and runs its own resolvers has at least been designed for this — verify it anyway. If cost is the constraint, the options that cost nothing, and what each gives up beats a free tier chosen at random.

Mistakes That Give False Results

A wrong result is worse than no result, because you act on it. These produce a confident, incorrect answer, and most are a false positive rather than a missed leak.

Testing too early is the most common. Give the client a few seconds after it reports "Connected" before you check anything; the moment of establishment is not the protected state. Testing on a corporate or campus network is the second.

Those networks intercept DNS at the network edge. A working tunnel should carry your DNS past that interception, so treat a leak there as something to investigate rather than something to dismiss.

Split tunneling produces the most convincing false alarm. An application you deliberately excluded from the VPN — a torrent client included — will correctly show your real address. That is the feature working, not a leak. Check your own configuration first.

And one in the other direction. A geolocation database putting your VPN address in the wrong city is a database being out of date, not a leak. The provider name is the field that matters. A city a few hundred miles from the server you picked is ordinary, not evidence of anything.

Finally, do not stop at one passing check. The leaks are independent, and the whole point of the checklist is that passing the address check tells you nothing about the five that follow it.

How Often, and What It Is Worth

No schedule can be justified from evidence, so here is the reasoning instead. Configurations do not drift on their own; they break when something changes. Test after changes rather than on a calendar.

The changes that matter most are the client updating, the operating system updating, joining a network you have not used before, changing router or provider, and turning on any new privacy feature. Each of those can break a setup that worked yesterday. None of them announces that it has.

One case is worth a habit. A network you did not choose — a hotel, an airport, a conference room — is where a forced resolver or a blocked protocol is likeliest and where you are least likely to check. Two minutes on the address and DNS tests covers most of it.

Beyond that, match it to what you are protecting. Occasional privacy needs an occasional check; work where exposure has real consequences needs one before the work, not after it. A daily routine is the kind that gets abandoned in the second week.

The Short Version

A VPN reporting "Connected" is telling you the tunnel exists, not that everything is inside it. Four things leak independently: the address your torrent client announces, your DNS queries, the addresses your browser offers over WebRTC, and your IPv6 traffic. A fifth exposure happens when the tunnel drops and nothing blocks the gap. Before any of them, the address check tells you whether the tunnel is working at all.

Check for a torrent IP leak first, because it is the only check that asks a different program, then work through the browser side in order and treat the provider name rather than the city as the field that decides a pass. Rule out split tunneling and a network with its own resolvers before you conclude anything. A passing browser test says nothing at all about what your client announces.

The one thing this page will not do is tell you which service to trust. Leak behavior changes with every release, and a result you produced yourself today is worth more than any recommendation, including one on this site. Why a private window changes none of this covers the mode people most often reach for instead, and the nine things a VPN still cannot hide covers the exposures that no leak test will ever catch.