Table of contents

Introduction: Why Your Proxy Can Be Perfect and You're Still Being Seen

Picture this. You bought a high-quality mobile proxy, configured your antidetect browser, checked your IP on three different services — every single one shows a mobile carrier address in the right region. You launch your ad account, warm up your profiles, run your scraping. A few days later, you get blocked for suspicious activity. Sound familiar? One of the most underrated causes of these stories is a DNS leak — DNS queries escaping outside the proxy.

The paradox is that your IP address really is spoofed. The site sees traffic from a mobile carrier. But before every connection, your computer quietly asks its own ISP: "where is such-and-such server?" And that question goes out directly, with no proxy involved. The result: the observer gets two pictures that don't add up. The connection comes from a mobile network in one region, but names are resolved through a home ISP's resolver in a completely different city. For anti-fraud systems in 2026, that discrepancy isn't a minor detail — it's one of the most reliable signals out there.

Based on our observations of support requests, a significant share of complaints like "the proxy doesn't work, geo is detected wrong, accounts keep dying for no reason" turn out, on closer inspection, not to be a proxy problem at all. It's a DNS-layer problem on the client side. And the number of people who deliberately check DNS before starting work is still a minority — most just check the IP.

In this guide, we'll cover the topic in full. You'll learn how name resolution works and at what point it bypasses the proxy. You'll understand how HTTP and SOCKS proxies differ when it comes to DNS, why a single letter in a connection string decides everything, and how browsers with encrypted DNS enabled create a whole new category of leaks. We'll give you four practical methods — diagnostics, client software configuration, browsers and antidetects, and the system level — each with step-by-step instructions and checklists. We'll cover common mistakes, case studies with numbers, and answer the tough questions.

One important boundary: this article is about the DNS layer. Leaks via WebRTC, browser fingerprints, timing, and other deanonymization channels are separate topics covered in other blog posts. Here, we focus on one, but a fundamental, channel — because without understanding it, all your other configuration rests on sand.

The Basics: How DNS Works and What a DNS Leak Is

The Internet's Phone Book

Every time a browser or script wants to connect to a site, it needs not a domain, but an IP address. The domain is a human-readable name. The address is network-readable coordinates. The service that translates one into the other is called DNS (Domain Name System). The simplest analogy is a phone book: you know the name, the book gives you the number. Except this book is distributed across thousands of servers and works in milliseconds.

Here's what name resolution looks like in practice:

  1. The application calls a system function (in the Unix world, usually getaddrinfo), passing it the domain name.
  2. The operating system checks the local cache and the hosts file.
  3. If there's no answer, the OS stub resolver sends a query to the DNS server address configured in the network settings. Usually, that's your ISP's server, handed out via DHCP, or a public resolver you set manually.
  4. The ISP's recursive resolver walks the chain of root servers, domain zone servers, and authoritative name servers, finds the answer, and returns it to you.
  5. The application gets the IP and only then establishes the connection.

Note the order. DNS first, connection second. A proxy is a tool that intervenes in the connection. Whether it intervenes in DNS depends on the proxy type, the protocol, and exactly how the application uses it.

What Exactly Counts as a Leak

DNS leak is a situation where application traffic goes through the proxy, but name resolution queries don't. They go out directly from your real network interface to the resolver configured in your system. The result: the site you're connecting to sees the proxy's IP, but your ISP and the resolver's owner see a list of every domain you've queried. And the target service, under certain conditions, can match where the connection came from with where the DNS query came from.

Why does this matter specifically for mobile proxy users? Because the whole value of a mobile IP is its plausibility. The address belongs to a cellular carrier, has thousands of real subscribers behind it, rotates, and has a good reputation. But a real mobile network subscriber resolves names through that same carrier's DNS servers. If your traffic exits from a mobile network while names resolve through a cable ISP in another region, you stop looking like a real subscriber. You start looking like someone using a proxy. Which you are — and you just told on yourself.

Three Parties Who See Your Leak

  • Your ISP. It sees the queries to its resolver and knows which domains you visit, even if the content itself went through the proxy.
  • The resolver's owner. If you set a public DNS, its operator sees the full list of your domains and your real IP.
  • The target site and its anti-fraud. It doesn't receive the DNS query directly, but there are indirect channels: geolocation of authoritative servers, EDNS Client Subnet, CDN routing, and special test domains generated for a specific session. More on this in the next section.

Deep Dive: The Anatomy of a DNS Leak When Working Through a Proxy

HTTP Proxy: Why It Usually Doesn't Leak, But Sometimes Does

When working through an HTTP proxy, the browser sends it a request with the domain in plain text. For unencrypted HTTP, it's the full URL in the first line of the request. For HTTPS, the browser sends a CONNECT command with the hostname and port, and the proxy resolves that name itself and establishes the tunnel. In both cases, the client doesn't need to know the target server's IP. Resolution is done by the proxy, on its side, with its resolvers. In the case of a mobile proxy — on the modem or phone side, through the carrier's DNS servers. That's how it should be.

So where do HTTP proxy leaks come from? Their sources are indirect:

  • PAC scripts. A proxy auto-config file may contain a dnsResolve function that resolves the domain locally to decide whether to route the request through the proxy. The decision itself is made after the local DNS query.
  • Pre-resolution of names. Some applications check host availability before connecting: ping, resolve, then go through the proxy. Java apps with InetAddress, some scrapers, link-checking plugins.
  • Browser background services. Page prefetching, DNS-prefetch, Safe Browsing checks, and update checks can operate on their own rules and don't always respect proxy settings.

SOCKS: One Letter Between a Clean Session and a Leak

Here's where it gets interesting. The original SOCKS4 protocol can only pass an IP address to the proxy. That means the client must resolve the name itself, before connecting. The leak is baked into the protocol. The SOCKS4a extension added hostname support. SOCKS5 supports three destination address types: IPv4, IPv6, and domain name.

You'd think SOCKS5 solves the problem. But support for a domain name in the protocol doesn't mean the client will use it. Many libraries and programs resolve the name locally by default and send the proxy an already-resolved IP. The protocol allows it — the leak just happens one step earlier.

Hence the famous letter h. In curl and libraries that follow its convention, the scheme socks5:// means local name resolution, while socks5h:// means passing the hostname to the proxy server for remote resolution. One letter. The difference between a clean session, where everything including DNS exits from the carrier's mobile network, and a session where every name first leaks to your ISP.

Why the Proxy Server Should Resolve Names Itself

There's a non-obvious point here that many people miss. It's not just about privacy. When the remote side of a mobile proxy resolves the name, the DNS answer is formed based on the carrier's location. Large services use CDNs and geo-DNS: the same domain returns different IPs to different clients, closest to them. If your home ISP resolves it, you get a CDN node address near your real location. Then you connect to that node through a mobile proxy from another region. To the service, this looks odd: a client from the mobile network of region A somehow hit a node intended for region B. This is the indirect DNS leak detection channel that doesn't require any access to your DNS queries.

EDNS Client Subnet: How the Resolver Gives Away Your Subnet

The EDNS Client Subnet (ECS) mechanism was designed so public resolvers could pass part of the client's address to authoritative servers — usually the first 24 bits for IPv4. This way a CDN knows where the real user is and returns the nearest node. It's great for speed. But from a leak perspective, it means that when resolving locally through a public DNS that supports ECS, the target domain's authoritative server receives your real connection's subnet. Not the full address, but enough to identify the ISP and city. Then the connection arrives from a mobile IP. Two subnets, two carriers, one user.

Encrypted DNS: A New Category of Leaks

Since the 2020s, browsers and operating systems have been shifting en masse to DNS over HTTPS (DoH) and DNS over TLS (DoT), and by 2026, DNS over QUIC joined the party. The idea is well-meaning: your ISP can no longer see your queries. But for proxy work, a side effect appeared. A browser with "secure DNS" enabled queries the chosen DoH server with its own client, and that traffic doesn't always follow the proxy settings. So names resolve not at the mobile carrier, but at a large public resolver — and from your real IP. Encryption protects you from the ISP, but not from the discrepancy between the DNS side and the connection side.

An additional layer of complexity comes from Encrypted Client Hello (ECH). For it to work, the browser requests special HTTPS records in DNS. The more sites use ECH, the more DNS queries the browser makes — and the more room for a leak if DNS isn't going down the right path.

IPv6 and Happy Eyeballs

Modern systems request both A records (IPv4) and AAAA records (IPv6) simultaneously and try to connect to whichever responds faster — the Happy Eyeballs algorithm. If your real network supports IPv6 while the proxy only works over IPv4, many applications can go directly over IPv6, bypassing the proxy entirely. Strictly speaking, this is a connection leak, not a DNS leak — but the trigger is precisely a DNS answer with an AAAA record. So in the context of DNS hygiene, IPv6 needs to stay on your radar.

Cache and Hosts: A Leak from the Past

The OS caches DNS answers. If you were working without a proxy and then turned one on, some names are already cached with addresses obtained through your home resolver. No new queries occur, but connections go to "home" CDN nodes. Same with the hosts file: entries there override name resolution entirely, and the proxy has no idea.

Method 1. Diagnostics: How to Test for a DNS Leak Yourself

Before configuring anything, you need to see the problem. The good news: a DNS leak test is a five-minute procedure you can — and should — turn into a ritual before every work session.

How Online Tests Work

Every DNS leak testing service works the same way. The page generates several unique subdomains like random-string.test-domain and forces your browser to resolve them, usually by loading invisible images or scripts. Since the subdomains are unique, they're definitely not in any cache. The query necessarily reaches the authoritative server of the testing domain, which belongs to the service. It records the IP from which the query came — that's the recursive resolver you're using. The page then shows you two columns: the address from which the HTTP connection came, and the resolver addresses. If the connection is from a mobile carrier while the resolver belongs to your home ISP or a public DNS service — you have a leak.

It's important to understand: any site can do the same thing. The mechanism doesn't require special privileges. Anti-fraud systems at major platforms use similar techniques as part of session risk scoring. This isn't a conspiracy theory — it's standard engineering.

Step-by-Step Testing Procedure

  1. Establish a baseline. Disable the proxy, open a DNS leak test, and note which resolvers appear. That's your "home" fingerprint. You should recognize it at a glance.
  2. Clear the DNS cache. In Windows, the command is ipconfig /flushdns; in macOS, restart the mDNSResponder service; in Linux, it depends on the resolver (e.g., resolvectl flush-caches for systemd-resolved). Restart the browser — it has its own cache.
  3. Enable the proxy the way you'll actually be working: through an antidetect profile, an extension, system settings, or code.
  4. Run an extended test that makes not one but dozens of checks. Leaks can be partial: nine out of ten queries go through the proxy, the tenth goes direct. A single test will miss that.
  5. Compare. All resolvers should belong to the cellular carrier the proxy runs through, or to the proxy service's infrastructure. Not a single address from the baseline. Not a single public resolver you didn't consciously choose.
  6. Test IPv6 separately. If the test shows any IPv6 address not belonging to the proxy — that's a leak.
  7. Repeat after ten minutes of work. Some background processes start with a delay.

Testing Without Third-Party Services: Your Own Test Domain

For those running account farms or scraping at industrial scale, it makes sense to have your own tool. The scheme: register an inexpensive domain and set up an authoritative DNS server for it on your VPS with query logging enabled. Then, in any project, at the start of any session, you query a unique subdomain like session-ID.your-domain. The DNS server log shows: which subdomain was queried and from which resolver IP. Match it with the session ID, and you instantly see which session, which profile, which worker leaked. This turns a one-off check into continuous monitoring.

Low-Level Testing: Watching the Network

The most honest way is to see what actually leaves the network interface. Run a traffic analyzer (Wireshark or tcpdump) on the machine's physical interface and filter for port 53 UDP and TCP, as well as port 853 for DoT. Then work through the proxy for five minutes. In an ideal world, the filter stays empty: all names are resolved on the proxy side, no local DNS packets at all. If there are packets, you immediately see which domains go where. For DoH, filtering is trickier because it's regular HTTPS on port 443 — but a good hint is connections to known public DoH provider addresses appearing without going through the proxy.

Diagnostics Checklist

  • Baseline without proxy recorded.
  • OS and browser cache cleared before testing.
  • Extended test with dozens of queries completed.
  • All resolvers match the proxy side.
  • No foreign-network IPv6 addresses.
  • Repeat test after 10 minutes of work passed.
  • For critical projects: traffic analyzer shows zero packets on port 53.

Method 2. Correct Client Software and Code Configuration

You've found the leak. Now you need to figure out exactly where the application decides to resolve names locally and switch it to remote resolution. Let's cover the most common environments from the practice of affiliates and developers.

The Principle: The Hostname Must Reach the Proxy

One rule, and it's universal. The proxy must receive the domain name from you, not an IP. For an HTTP proxy, this happens naturally. For SOCKS5, you explicitly need to choose remote DNS mode. For SOCKS4 without the a extension, it's impossible — such proxies are unusable for clean work. Modern mobile proxy services support both HTTP and SOCKS5 with remote resolution, so the limitation is purely on the client side.

curl and the Command Line

For SOCKS5, always use the scheme with the letter h. Example of a correct call:

curl -x socks5h://user:pass@host:port https://example.com/

Without the h, curl resolves the name locally. This applies to all tools built on libcurl. For HTTP proxies, the http:// scheme in the -x parameter is enough: the name goes in the CONNECT request.

Python: requests, httpx, aiohttp

In the requests library with the SOCKS support package installed, the same rule applies: socks5:// means local resolution, socks5h:// means remote. This is the most common mistake in scrapers: a developer copies a documentation example with socks5 and runs traffic with a DNS leak for years without suspecting a thing. In httpx and aiohttp, SOCKS support is implemented via third-party transports, and remote resolution mode needs to be verified in the specific transport's docs — sometimes it's an rdns parameter, sometimes the h scheme again. Verify not against the docs, but in practice: run the script against your own test domain and check the log to see where the query came from.

A separate trap: low-level socket libraries that monkeypatch the standard socket module to route all traffic through SOCKS. They have a remote-resolution flag, but it's not uncommonly off by default. Plus, any call to socket.gethostbyname in your code or dependencies will bypass it and resolve the name through the system resolver.

Node.js and Headless Browsers

In the Node.js ecosystem, SOCKS agents usually pass the hostname to the proxy, but it depends on the specific package and version. For Puppeteer and Playwright, the proxy is set at browser launch, and behavior is inherited from the Chromium engine — we'll discuss its SOCKS5 quirks in the next section. If you're using the HTTP mode of a mobile proxy, the issue disappears: Chromium sends CONNECT with the hostname.

Go, Java, and Other Languages

In Go, the standard package golang.org/x/net/proxy for SOCKS5 passes the hostname remotely — but only if you use its Dialer directly, not resolving beforehand. In Java, system properties for SOCKS proxies work, but many HTTP clients construct an InetSocketAddress with pre-resolution, which causes the leak. The fix is to create an unresolved address (methods like createUnresolved) and ensure the client supports hostname passing. Universal advice for any language: find every place in your code and dependencies where a domain turns into an IP, and make sure that happens after establishing the proxy connection, not before.

Step-by-Step Project Audit

  1. Find every connection string to the proxy in your code. Check the schemes: socks5 without h — red flag.
  2. Find every explicit name-resolution call: gethostbyname, getaddrinfo, dns.lookup, InetAddress.getByName. Each one is a potential leak.
  3. Check dependencies: availability-check libraries, health-checks, retries with pre-pings.
  4. Run the project against your own test domain with a unique subdomain per worker. The DNS server log shows who's leaking.
  5. Add an automated test: a session isn't valid until the DNS check confirms the resolver belongs to the proxy side.
  6. Document the result in the project docs: which library, which version, which mode.

Developer Checklist

  • All SOCKS5 connections use remote resolution.
  • No pre-resolution before connecting.
  • Libraries verified not by documentation but by test-domain log.
  • Automated DNS check built into session start.
  • For HTTP proxy mode, verified that CONNECT is used, not an IP substitution.

Method 3. Browsers and Antidetect Browsers Without DNS Leaks

Most mobile proxy users work not in code but in a browser: ad accounts, social networks, marketplaces, multi-accounting. Here the rules are different, and they vary from engine to engine.

Firefox and Its Descendants

Firefox has historically offered the most transparent control. The key parameter in about:config is network.proxy.socks_remote_dns. When set to true, names are passed to the SOCKS proxy for remote resolution. When false, they resolve locally. In many older builds and profiles, it's off. The second parameter is network.trr.mode, which controls encrypted DNS: a value of 5 disables it entirely, which is preferable for proxy work because otherwise the browser may query a DoH server with its own client. The third block is prefetching: network.dns.disablePrefetch set to true and network.predictor.enabled set to false disable speculative name resolution for links on the page, which would otherwise go around the proxy before the actual click. Antidetect browsers on the Firefox engine usually set these parameters correctly, but it's worth checking after every update.

Chrome, Chromium, and Antidetects Built on Them

With Chromium, the story is more complicated. Working through an HTTP proxy, it sends CONNECT with the name — no leak. But when using a SOCKS5 proxy via launch flag, the engine resolves names locally in a number of configurations, and there's no standard "remote DNS" setting in the UI. A well-known engineering trick is the --host-resolver-rules flag with a rule that maps all names to a "not found" state, excluding the proxy address itself. As a result, the local resolver can't resolve anything, and the browser is forced to pass names to the proxy. It looks like a hack, but it works reliably. A second important point is the secure DNS setting in the privacy section: when enabled, Chromium uses DoH to the chosen provider, and that traffic doesn't always follow the proxy. For mobile proxy work, disable it or verify through tests that it's properly tunneled. Third is page prefetching: the performance settings have a preload option that initiates DNS queries for links you haven't clicked yet.

What an Antidetect Browser Should Be Able to Do

A good antidetect handles all this routine for you. But implementation quality varies greatly. Here's what to check when choosing one and after every update:

  • Remote DNS mode for SOCKS5 enabled by default for each profile, not globally.
  • DNS isolation between profiles. The name-resolution cache must not be shared: otherwise a profile on a mobile proxy in one region gets an IP cached by a profile on a proxy in another region.
  • Disabled or tunneled encrypted DNS. Ask support directly: how does the built-in DoH behave when working through a proxy?
  • Disabled prefetch. Speculative resolution shouldn't live in a profile pretending to be a regular mobile user.
  • Built-in check for DNS leaks at profile start, or at least convenient access to a test.
  • Behavior on proxy failure. What does the browser do if the proxy is unavailable: block connections or go direct? The latter is a catastrophe not only for DNS.

Proxy Extensions: Thin Ice

Browser extensions that switch proxies work through the browser API. They can set the proxy for connections, but their control over DNS is limited by the engine's capabilities. An extension can't force Chromium to use remote DNS for SOCKS5 if the engine itself doesn't do so in that configuration. Plus, an extension doesn't manage the browser's background services. So extensions are an acceptable option for HTTP mode of a mobile proxy and quick checks, but not for serious work with sensitive accounts.

Step-by-Step Profile Setup

  1. Create a profile and specify the mobile proxy. Prefer HTTP mode if the antidetect doesn't guarantee remote DNS for SOCKS5.
  2. Disable encrypted DNS in the engine or profile settings.
  3. Disable page prefetching and DNS-prefetch.
  4. If it's a Firefox-like engine, check socks_remote_dns manually.
  5. Launch the profile, clear the cache, and run an extended DNS leak test.
  6. Browse a few sites with active analytics and repeat the test: did any new resolvers appear?
  7. Save the result as a reference for this profile.

Method 4. System Level and Infrastructure: Forcing Leaks Shut

All previous methods rely on trust: we configure the application and hope it behaves correctly. The engineering approach is different: make the leak technically impossible. Even if an application tries to send a DNS query directly, it shouldn't get out.

The "Everything Not Through the Proxy Is Forbidden" Principle

On a work machine or farm server, a firewall is configured to block outbound traffic on port 53 (UDP and TCP) and port 853 for all processes except explicitly allowed ones. On Windows, this is outbound rules in the firewall; on Linux, nftables or iptables; on macOS, pf. The point: if a browser or script tries to resolve a name locally, it gets an error instead of a silent leak. An error is immediately visible — you'll see it and fix the application config. A silent leak can live for months.

The DoH subtlety: it goes over port 443, which you can't block entirely. The solution is to block not the port, but the addresses of known public DoH resolvers for processes that should only go through the proxy. This requires maintaining a list, but the list changes rarely.

Isolation via Containers and Network Namespaces

For developers and farm owners on Linux, the most powerful tool is network namespaces and containers. The idea: each worker, each browser profile or group of profiles lives in its own network namespace that has no default route to the internet at all. The only way out is the proxy address. Whatever the application tries — resolve a name, go out over IPv6, open a direct connection — it physically has no route. This is the most reliable way to guarantee the absence of DNS leaks at scale. In Docker, this is achieved with a user-defined network without an external gateway plus explicit access only to the proxy address. Additionally, you can set a deliberately unreachable address in the container's resolver config so any local resolution attempt fails instantly rather than hanging on a timeout.

IPv6 at the System Level

If your mobile proxy works over IPv4 while the machine has IPv6 connectivity, the simplest and most reliable solution is to disable IPv6 on the interface used by proxy profiles, or block outbound IPv6 at the firewall. Yes, it's crude. But it eliminates a whole class of problems where an AAAA record in a DNS answer routes the connection directly.

The System Resolver and Its Quirks

Modern OSes have multi-layered resolvers. Windows 11 supports DoH at the system level, and if it's enabled for your adapter, all local resolutions will go to the chosen DoH server. For a work machine with a proxy, you need to be aware of this: enabling system DoH changes the leak picture but doesn't eliminate it. Android uses the Private DNS feature — a similar story for those working with proxies on mobile devices or emulators. On Linux with systemd-resolved, check which DNS servers are assigned to each interface, because the resolver can route queries by domain suffix between interfaces, and this creates unexpected paths.

Monitoring as a Process

At the infrastructure level, DNS leak checks turn from one-off into continuous. What's worth implementing:

  • Logging of blocked DNS attempts by the firewall. Each log entry is an application trying to resolve locally. That's your fix list.
  • Your own test domain with unique subdomains per session and an automatic alert when a foreign resolver appears.
  • Periodic network traffic snapshots on port 53 from the physical interface — daily, automatically, with an alert on any non-zero count.
  • Verification after every update of the browser, antidetect, libraries. Updates are the main source of regressions: developers change defaults, enable new prefetch features, add encrypted DNS.

System-Level Checklist

  • Outbound traffic on ports 53 and 853 blocked for work processes.
  • Known public DoH addresses blocked for the same processes.
  • IPv6 disabled or blocked on work interfaces.
  • Critical workers isolated in network namespaces with no direct route.
  • Firewall DNS logs collected and reviewed.
  • Test domain and alerting configured.

Common Mistakes: What Not to Do

Mistake 1. Checking Only the IP

The most widespread. A person sees a mobile carrier address on the IP check page and considers the job done. But the IP check only answers "where did the connection come from," not "where did the DNS queries come from." These are different questions with different answers.

Mistake 2. Setting a Public DNS and Calling It a Day

The logic is clear: if the ISP sees my queries, I'll set a public resolver. But for proxy work, this isn't a solution — it's swapping one leak for another. The queries still go out from your real IP, now to a different observer. And public resolvers actively use ECS and pass your subnet to authoritative servers. The discrepancy between the DNS side and the connection side remains.

Mistake 3. Using SOCKS5 Without Remote DNS

The socks5 scheme instead of socks5h in code, socks_remote_dns turned off in the browser, an antidetect with default local resolution. Thousands of projects have lived with this mistake for years.

Mistake 4. Treating Encrypted DNS as a Solution

DoH protects the content of queries from the ISP. But when working through a proxy, it creates a separate channel that doesn't go through the proxy. Encryption isn't the same as correct routing.

Mistake 5. Ignoring Prefetch and Background Services

The browser resolves names of links you haven't opened yet. The antivirus checks URLs. The updater looks for an update server. All of these are DNS queries that can go around. A single test doesn't catch these things.

Mistake 6. Shared DNS Cache Between Profiles

If two profiles on proxies in different regions share a cache, the second profile connects to a CDN node chosen for the first region. Profile isolation must include DNS.

Mistake 7. Not Testing After Updates

A new browser version enabled secure DNS by default. An updated library changed SOCKS behavior. An antidetect update reset engine settings. These are all real scenarios that only get uncovered by re-testing.

Mistake 8. Allowing Direct Exit When the Proxy Is Unavailable

Settings like "if the proxy doesn't respond, go direct" turn any failure into full session deanonymization, starting with DNS. The correct behavior is to block connections until the proxy is restored.

Mistake 9. Manual Resolution "for Speed"

Some scrapers resolve a domain once and then go by IP to save on DNS. Besides leaking the query itself, they get an IP chosen by geo-DNS for their real region and then run traffic through a mobile proxy to a "foreign" CDN node. Saving milliseconds results in an inconsistent profile.

Tools and Resources

Online Leak Tests

DNS leak testing services come in basic and extended versions. Basic ones make one or two queries and are good for a quick estimate. Extended ones generate dozens of unique subdomains and reveal partial leaks. For work, choose the ones that show not only the resolver IP but also its affiliation: organization, autonomous system, country. A good test also shows IPv4 and IPv6 separately and can check behavior on repeat queries.

Traffic Analyzers

Wireshark — a graphical analyzer with filters like dns or udp.port == 53. tcpdump — the console equivalent for servers and Linux machines. Both let you see the truth: what actually leaves the network interface. For DoH, additionally watch TLS connections to public resolver addresses.

Your Own Authoritative DNS

For monitoring at scale: any lightweight DNS server with query logging (CoreDNS, Unbound in authoritative mode, BIND, compact Go or Python servers) plus your own domain. Minimal cost, and the result is constant oversight of all workers and profiles.

Command-Line Tools

dig and nslookup show which resolver the system is querying and what it returns. resolvectl on Linux with systemd-resolved shows DNS configuration per interface. curl with the verbose flag shows whether it passes the name to the proxy or resolves it itself. On Windows, ipconfig /displaydns shows the cache contents, and Get-DnsClientServerAddress in PowerShell shows assigned servers per adapter.

Firewalls

The built-in Windows Firewall with per-program rules, nftables and iptables on Linux, pf on macOS. For convenience managing per-application rules, graphical frontends exist. The key requirement is the ability to block ports for specific processes and log blocks.

Containerization

Docker and Podman with user-defined networks, Linux network namespaces via ip netns, and for browser farms — profile orchestrators that support per-profile network isolation. They turn the "only through the proxy" rule from a setting into an architectural guarantee.

Proxy Service Capabilities

Pay attention to what the mobile proxy provider itself offers: SOCKS5 support with remote name resolution, HTTP mode with correct CONNECT handling, DNS stability on the carrier side, no DNS answer substitution on the infrastructure side. It's useful to ask support which resolvers names are resolved through during remote resolution — the correct answer: through the mobile carrier's resolvers whose network the modem is connected to.

Case Studies and Results

Case 1. An Ad Account Farm and the Invisible Cause of Bans

A team of affiliates was running about 120 ad accounts on mobile proxies through a popular antidetect. The average account lifespan before blocking held at 9–12 days with seemingly flawless setup: mobile IPs in the right region, careful fingerprints, warming. The audit showed that after a routine antidetect update, encrypted DNS had been enabled in the engine, and all profiles were resolving names through the same public DoH resolver from the office's real IP. 120 "independent" users from different cities were resolving names from a single point. After disabling DoH, enabling remote DNS, and blocking port 53 at the firewall, the average account lifespan grew to 30+ days and the share of early bans in the first week dropped roughly threefold. The cost of the fix was two hours of one specialist's time.

Case 2. A Marketplace Scraper and Mysterious Geo Prices

A developer was collecting prices from a large marketplace by region through mobile proxies from different cities. The data didn't match what real users in those regions saw: some prices and availability corresponded to a completely different city. The cause turned out to be the connection string: the requests library with the socks5 scheme without h. Names were resolving locally in the developer's city, the marketplace's geo-DNS returned a node for his region, and subsequent requests through a mobile proxy from another city arrived at a "foreign" node that served regional results by its own logic. Changing one letter in the config and adding an automatic DNS check at each worker's start restored data accuracy. A side effect: the share of requests answered with a captcha dropped — sessions became more consistent.

Case 3. Testing Ads for Regional Audiences

A marketing agency was checking how ads and landing pages displayed to users in different regions, working through mobile proxies and a Chromium browser with SOCKS5 connections. Some checks showed content from the wrong region. In the agency's own test domain logs, the resolvers belonged to the office ISP. Switching to HTTP mode on the same mobile proxies — where Chromium passes names via CONNECT — plus disabling page prefetching eliminated the discrepancy. An added bonus: stable check results without re-runs saved the team about 15 percent of time on regular audits.

Case 4. Social Media Multi-Accounting and a Shared Cache

An operator of dozens of social media accounts noticed that accounts working on the same day started getting blocked in groups. The investigation revealed two DNS-layer factors: the antidetect used a shared DNS cache between profiles, and some profiles were on SOCKS5 without remote resolution. The result: profiles on proxies in different regions connected to the same CDN nodes, and some also resolved names from a single real IP. After enabling per-profile cache isolation and switching all connections to remote DNS, group blocks stopped; over the following two months, account losses returned to levels typical of careful manual work.

The Common Takeaway from the Cases

In all four stories, the proxies were working fine. The problem lived on the client side and cost weeks of work, budgets, and accounts. The fix each time took hours. That ratio is a hallmark of DNS leaks: the problem is invisible without a special check, but easily fixed once you know where to look.

FAQ: Tough Questions About DNS Leaks

If the Site Doesn't Receive My DNS Queries, How Does It Even Know About the Leak?

Three indirect paths. First — unique test subdomains: a site can force your browser to resolve a domain it controls and see which resolver the query came from. Second — geo-DNS and CDNs: if you arrive at a node intended for a different region, that discrepancy with your IP is visible on the infrastructure side. Third — EDNS Client Subnet: public resolvers pass the client's subnet to authoritative servers, and it doesn't match the connection's subnet. None of these paths require access to your ISP.

The Mobile Proxy Resolves Names Through the Carrier. Is That Good or Bad?

It's ideal for plausibility. A real cellular subscriber resolves names through the carrier's resolvers, and their connections come from addresses of the same carrier. When your proxy does the same, the DNS side and the connection side belong to the same network. That's exactly the state you should see in tests: carrier resolvers, carrier IP, one region.

Why Is the Mobile Proxy's HTTP Mode Better Than SOCKS5 for DNS?

Because in HTTP mode, the hostname is passed to the proxy by protocol definition — in CONNECT for HTTPS and in the URL for HTTP. The client can't accidentally resolve the name locally, except in exotic cases like PAC scripts. In SOCKS5, remote resolution is an option the client must explicitly choose, and many clients don't do so by default. If you're not sure about a specific browser or library's behavior, HTTP mode is safer. SOCKS5 is more convenient for non-HTTP protocols, but it requires control.

Is Simply Disabling Secure DNS in the Browser Enough?

No. That closes one channel — the browser's DoH. What remains: local resolution for SOCKS5, prefetch, background services, system DoH, and IPv6. Disabling secure DNS is a necessary but insufficient step. Only confirmation by an extended test, and ideally blocking direct DNS at the system level, is sufficient.

What Should I Do If Resolvers Appear in the Test That Belong Neither to Me Nor the Carrier?

Investigate step by step. First, identify the organization by IP: if it's a public DNS service, look for enabled DoH in the browser or system. If it's an unknown hosting provider, the proxy infrastructure might be using its own resolvers instead of the carrier's — check with the provider. If it's your ISP but not the resolver you saw in the baseline, it might be IPv6 or another adapter. Every unexpected resolver has an explanation, and you need to find it, not ignore it.

Does a DNS Leak Affect Speed When Working Through a Proxy?

It does, and often in an unexpected direction. With local resolution, geo-DNS picks a CDN node near your real location, and traffic then goes through a mobile network in another region to that node — the route ends up longer than optimal. With remote resolution, the node is chosen near the proxy exit, and the path from the proxy to the server is shorter. So proper DNS configuration usually doesn't slow things down — in some cases it actually speeds up loading.

How Do I Test for DNS Leaks in Automated Scenarios Without a Browser?

The most reliable path is your own test domain. At each worker's start, the script queries a unique subdomain through the proxy, and your authoritative DNS server logs which resolver the query came from. The script then reads the log via API and compares the resolver address with the expected carrier range. If there's no match, the session doesn't start. This turns the check from manual into contractual: a worker isn't allowed to run until it's proven DNS cleanliness.

How Is the Picture Changing with the Spread of ECH and Encrypted DNS in 2026?

The landscape is moving toward "DNS becomes more important." ECH depends on HTTPS-type DNS records, browsers enable encrypted DNS by default, operating systems add system DoH and DoQ. For a regular user, this is a privacy plus. For those working through proxies, it means more DNS traffic, more independent DNS clients inside the system, and more points where a query can escape the proxy. Anti-fraud systems, in turn, are increasingly using consistency between the DNS side and the connection side as a signal. The takeaway: DNS discipline is shifting from "desirable" to "mandatory."

Can I Trust an Antidetect Browser That Claims DNS Leak Protection?

Trust — yes; verify — always. Marketing claims don't override regressions after updates, differences between engines, and the specifics of your proxy configuration. Test every profile after creation and after every browser update. One extended test takes a minute, while recovering a burned farm takes weeks.

Conclusion: DNS as the Foundation of a Clean Session

Let's sum up. A proxy changes the address the connection comes from but doesn't guarantee that name resolution takes the same path. The DNS query happens before the connection, and that's exactly where a DNS leak is born. For mobile proxy users, this is especially critical: the whole value of a mobile IP is its resemblance to a real subscriber, and a real subscriber resolves names through their carrier. A discrepancy between the DNS side and the connection side reveals proxy usage more reliably than many other signals.

We've covered how DNS leaks in different scenarios: SOCKS without remote resolution, encrypted DNS in browsers and systems, prefetching, shared cache, IPv6, PAC scripts, and pre-resolution in code. We gave four methods that work together: diagnostics with a baseline and extended test, proper configuration of clients and libraries, browser and antidetect setup, and finally forced protection at the firewall and network isolation level. Each method alone closes part of the problem. Together, they make the leak technically impossible.

Your Next Steps

  1. Today: capture a baseline without a proxy, then run an extended DNS leak test in every work profile and every script. Write down the results.
  2. This week: check all connection strings in your code for socks5 without h, disable encrypted DNS and prefetching in browsers, ensure cache isolation between profiles.
  3. This month: block direct DNS at the system level for work processes, disable or block IPv6 on work interfaces, set up your own test domain with logging.
  4. Continuously: repeat the check after every browser, antidetect, and library update. Turn it into a ritual, like checking your IP.

A good mobile proxy gives you a plausible address and plausible carrier resolvers. Your job is not to squander that advantage on the last mile, inside your own system. Configure DNS correctly once, make checking a habit, and a whole category of inexplicable blocks will simply disappear from your practice. Isn't that why you read this guide to the end?