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# DNS Leaks & IPv6: The Silent Privacy Killer You Didn't See Coming.
- URL: https://snubmonkey.com/dns-leaks-ipv6-the-silent-privacy-killer-you-didnt-see-coming/
- Published: 2025-06-05T21:16:40.000Z
- Updated: 2025-12-09T00:07:52.000Z
- Description: DNS leaks silently expose your browsing, even when using Pi-hole or a VPN. IPv6 makes it worse by bypassing your DNS filters. Learn how to fully block IPv6 DNS leaks at the router, system, and firewall level to ensure your privacy stays airtight.
- Author: yannick Coffi
- Tags: security 🦾🦿, how to 🪄, linux 🐧, tips, vpn💄🕸️

## **What Is a DNS Leak?**

When you type a website address like snubmonkey.com, your device sends a **DNS query** to resolve that domain into an IP address. Ideally, this request is handled securely by **your chosen DNS server** (like Pi-hole, Unbound, or a VPN tunnel).

But a **DNS leak** occurs when these DNS queries are sent **outside of your encrypted/private tunnel** — for example, to your ISP or a third-party resolver — even if the rest of your traffic is routed through a VPN or filtered by Pi-hole.

In short, a **DNS leak means others can still see what sites you're visiting**, even if the rest of your traffic is protected.

## **Why IPv6 Makes It Worse**

Even if you've locked down IPv4 DNS leaks, many networks and devices **still use IPv6 DNS resolvers by default** — especially if you haven't explicitly disabled IPv6\.   
This allows:

- Devices to **bypass Pi-hole** by using hardcoded or ISP-assigned IPv6 DNS
- DNS queries to leak directly over IPv6 — undetected by most users
- VPN users to **leak real browsing behavior** despite the VPN being active

##   
  
**How to Fully Prevent IPv6 DNS Leaks**  
  
### **1\. Disable IPv6 at the Router Level (Best Practice)**

Most modern routers offer an option to **turn off IPv6 entirely**:

- Log into your router's admin panel
- Look for **IPv6 settings** (often under LAN, WAN, or Advanced)
- **Disable IPv6 support**
- Reboot your router

### **2\. Disable IPv6 on the Pi-hole Server**

On your (Linux-based) machine; **at the operating system level**:

```
$ sudo nano /etc/sysctl.d/99-disable-ipv6.conf
```

Add:

```
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
```

Let's explain:

- net.ipv6.conf.\* are **kernel-level networking flags** that completely **disable the IPv6 protocol stack** on the system.

  
**net.ipv6.conf.all.disable\_ipv6 = 1**  
This disables **IPv6 on all current and future network interfaces**. It’s the most comprehensive setting — think of it as the “master switch” for IPv6 across your entire system.

**net.ipv6.conf.default.disable\_ipv6 = 1**  
This disables IPv6 **by default** for any **new network interfaces** that get created after boot (like a USB Ethernet dongle, VPN tunnel, or bridge).  
Without this, new interfaces might still come up with IPv6 enabled.

**net.ipv6.conf.lo.disable\_ipv6 = 1**  
This disables IPv6 on the **loopback interface** (lo), which is used for internal communications on the machine (127.0.0.1 or ::1).  
While not always critical, it’s good hygiene for fully disabling IPv6 support.  
  
Then apply:

```
$ sudo sysctl -p /etc/sysctl.d/99-disable-ipv6.conf
```

This disables IPv6 on all interfaces for the server itself.  
  
### **3\. Lock DNS to Pi-hole\* in etc/resolv.conf**

To prevent DNS leaks — especially when IPv6 is disabled — you must make sure your system **only uses your Pi-hole** (e.g. 192.168.1.1xx) as its DNS resolver.  
  
**Edit**: **`/etc/resolv.conf`**

```
$ sudo nano /etc/resolv.conf
```

Replace its content with:

```
nameserver [Your Pi-hole IP]
```

Make sure no other DNS servers (like 192.168.1.1 or IPv6 addresses like fe80::1%) are present.  
  
Lock the File:  
Prevent it from being overwritten by DHCP or NetworkManager:

```
$ sudo chattr +i /etc/resolv.conf
```

To unlock it later, run:

```
$ sudo chattr -i /etc/resolv.conf
```

### **4\. Block IPv6 DNS Traffic with Firewall (Optional; yet Powerful)**

If you're using UFW:

```
$ sudo ufw deny out to any proto ipv6
```

Or configure your router to block:

- UDP port **53** and **5353**
- TCP port **53**
- For IPv6 (only)

## **Test for DNS Leaks**

Use these tools to verify you're leak-free:

- [dnsleaktest.com](https://dnsleaktest.com/?ref=snubmonkey.com)
- [ipleak.net](https://ipleak.net/?ref=snubmonkey.com)
- [browserleaks.com/ip](https://browserleaks.com/ip?ref=snubmonkey.com)

You should see:

- Only IPv4 DNS servers
- Your Pi-hole's IP address
- No IPv6 addresses at all

DNS leaks are subtle but critical threats to that privacy, especially in a world slowly shifting toward IPv6\. By taking a layered approach — router, server, DNS stack, and firewall — you **shut down IPv6 leaks completely**, even on a modern, dual-stack network.  
  
We hope you found these insights useful!