Pi-hole Regex Deny Not Blocking? Here's How To Fix It

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Pi-hole Regex Deny Not Working? Here's How to Fix It

Hey guys, running into issues with your Pi-hole regex deny rules not blocking domains as expected? It can be super frustrating when you think you've set up a rule to block certain ads or trackers, but they still slip through. This article will dive into a common problem where regex deny rules in Pi-hole don't seem to work and give you a step-by-step guide on how to troubleshoot and fix it.

Understanding the Issue with Pi-hole Regex Deny

So, you've added a regex rule like _vungle\.com$_ to your Pi-hole, thinking it will block all domains ending with vungle.com. But to your surprise, domains like adx.ads.vungle.com or logs.ads.vungle.com are still getting through. What's happening here? It's a common head-scratcher for many Pi-hole users, but don't worry, we'll break it down.

The Importance of Regex in Pi-hole

Before we dive deeper, let's quickly touch on why regex is so powerful in Pi-hole. Regular expressions, or regex, allow you to create flexible and efficient filters. Instead of adding individual domains to your blocklist, you can use a single regex rule to block a whole range of domains that match a specific pattern. This is particularly useful for blocking ad networks or tracking services that use multiple subdomains. However, the power of regex also means that mistakes in your rules can lead to unexpected behavior. So, getting it right is super important!

Common Causes for Regex Deny Rules Not Working

There are several reasons why your regex deny rules might not be working as expected in Pi-hole. We'll cover the most common culprits in detail, but here's a quick rundown:

  1. Incorrect Regex Syntax: Regex can be tricky, and even a small mistake in your syntax can prevent the rule from working.
  2. Anchoring Issues: Forgetting to anchor your regex to the start or end of the domain can lead to unexpected matches (or misses).
  3. Caching Problems: Sometimes, Pi-hole's cache can cause delays in applying new rules.
  4. Rule Order: The order of your rules can sometimes affect whether a rule is applied.
  5. Misunderstanding Regex Matching: It's important to understand how regex matches domains to ensure your rule is doing what you expect.

Diagnosing the Problem: A Step-by-Step Guide

Okay, let's get our hands dirty and figure out why your regex rule isn't working. Here's a systematic approach to diagnosing the problem.

Step 1: Verify Your Pi-hole Setup

First, let's make sure your Pi-hole is set up correctly and that you're running the latest versions. Outdated software can sometimes have bugs that affect regex filtering.

  1. Check Pi-hole Version: Run pihole -v in your terminal to check the versions of Pi-hole, the web interface, and FTL (the DNS/DHCP server). Make sure you're on relatively recent versions. If not, consider updating.

    pihole -v

  2. Ensure Pi-hole is the DNS Server: Verify that your devices are actually using Pi-hole as their DNS server. You can check this in your device's network settings or by visiting a site like whatsmydns.net and checking the DNS server being used.

Step 2: Examine Your Regex Rule

Now, let's take a close look at the regex rule itself. This is where many issues tend to arise.

  1. Syntax Check: Double-check your regex syntax. Even a small typo can break the entire rule. Common mistakes include forgetting to escape special characters (like periods) or using the wrong quantifiers.

    • Escaping Special Characters: In regex, characters like ., *, +, ?, \, ^, $, {, }, (, and ) have special meanings. If you want to match these characters literally, you need to escape them with a backslash (\). For example, to match vungle.com, you should use vungle\.com.
    • Quantifiers: Characters like * (zero or more), + (one or more), and ? (zero or one) control how many times a character or group can appear. Make sure you're using the right quantifier for your needs.

  2. Anchoring: Anchoring your regex is crucial for precise matching. Anchors tell the regex engine where the match should start and end.

    • ^: Matches the beginning of the string.
    • $: Matches the end of the string.

    For example, vungle\.com$ will only match domains that end with vungle.com. If you want to block any domain containing vungle.com, you would use vungle\.com (without the $).

    In the original problem, the regex vungle\.com$ was intended to block domains ending with vungle.com. However, domains like adx.ads.vungle.com don't match this pattern because they don't end with vungle.com. To block these, you'd need to use a regex like vungle\.com (without the $ anchor) or .*vungle\.com.

  3. Testing the Regex: Use a regex testing tool to see if your rule matches the domains you expect. There are many online regex testers available (like Regex101) where you can input your regex and test strings to see the matches.

    Example:

    • Regex: vungle\.com$

    • Test String: adx.ads.vungle.com

    • Result: No match

    • Regex: .*vungle\.com

    • Test String: adx.ads.vungle.com

    • Result: Match

Step 3: Check Pi-hole's Query Log

The Pi-hole query log is your best friend for debugging. It shows you exactly which domains are being queried and whether they're being blocked or allowed.

  1. Locate the Query Log: Go to your Pi-hole web interface and navigate to the