How to Set Up a Secure DNS Sinkhole for Network Protection

Combine Pi-hole for domain blocking with dnscrypt-proxy for encrypted upstream queries to create a privacy-preserving DNS sinkhole that filters malicious traffic before it reaches your devices.

The trimstray/the-book-of-secret-knowledge repository aggregates battle-tested open-source tools for hardening network infrastructure. Setting up a secure DNS sinkhole for network protection requires orchestrating multiple components that handle resolution, filtering, and encryption to prevent ads, trackers, and malware domains from reaching client devices.

Core Components of a Hardened DNS Sinkhole

According to the source code analysis of README.md in trimstray/the-book-of-secret-knowledge, four primary tools form the foundation of a resilient DNS sinkhole:

• Pi-hole: Acts as the primary DNS server and sinkhole, answering queries for blocked domains with 0.0.0.0 or NXDOMAIN. The repository lists Pi-hole at line 759 as "a DNS sinkhole that protects your devices from unwanted content."
• dnscrypt-proxy: Provides encrypted upstream resolution using DNS-over-HTTPS (DoH) or DNS-over-TLS (DoT). Referenced at line 220 as "a flexible DNS proxy, with support for encrypted DNS protocols."
• Unbound: Optional recursive resolver that adds DNSSEC validation to prevent DNS spoofing. The repository cites an "Unbound DNS Tutorial" at line 1524.
• Community Blocklists: Curated lists of malicious domains (e.g., StevenBlack, Firebog) aggregated in the repository between lines 499-511 under DNS-related resources.

Deployment Architecture

A secure deployment chains these components so that client devices interact only with the sinkhole, while upstream queries remain encrypted and validated:

Client Devices → Pi-hole (Port 53) → dnscrypt-proxy (Port 5353) → Encrypted Internet DNS
                     ↓
              Blocklists (NXDOMAIN/0.0.0.0)

Traffic flow:

1. All client DNS queries route to Pi-hole on port 53.
2. Pi-hole checks its blocklist; matching domains return sinkhole addresses immediately.
3. Permitted queries forward to dnscrypt-proxy (listening on 127.0.0.1:5353) for encrypted upstream resolution.
4. Optional Unbound insertion between Pi-hole and dnscrypt-proxy adds DNSSEC validation before encryption.

Step-by-Step Implementation

1. Deploy Pi-hole as the Blocking Layer

Create a docker-compose.yml file that defines Pi-hole with persistent storage for configuration and blocklists. The container must expose port 53 to your LAN and depend on the dnscrypt-proxy service.

services:
  pihole:
    image: pihole/pihole:latest
    container_name: pihole
    environment:
      TZ: "UTC"
      WEBPASSWORD: "SecureAdminPassword"
      DNSMASQ_LISTENING: "all"
      PIHOLE_DNS_: "127.0.0.1#5353"
    volumes:
      - "./pihole/etc-pihole:/etc/pihole"
      - "./pihole/etc-dnsmasq.d:/etc/dnsmasq.d"
    ports:
      - "53:53/tcp"
      - "53:53/udp"
      - "80:80/tcp"
    restart: unless-stopped
    depends_on:
      - dnscrypt

Key configuration details:

• PIHOLE_DNS_: "127.0.0.1#5353" directs Pi-hole to forward uncached queries to the dnscrypt-proxy container.
• Volume mounts preserve blocklists and custom DNS settings across container restarts.

2. Configure dnscrypt-proxy for Encrypted Upstream

Add the dnscrypt-proxy service to your docker-compose.yml to handle DNS encryption. This prevents your ISP or network eavesdroppers from viewing DNS queries that pass the sinkhole filter.

  dnscrypt:
    image: jedisct1/dnscrypt-proxy:2
    container_name: dnscrypt-proxy
    volumes:
      - "./dnscrypt-proxy/dnscrypt-proxy.toml:/etc/dnscrypt-proxy/dnscrypt-proxy.toml"
    ports:
      - "5353:53/tcp"
      - "5353:53/udp"
    restart: unless-stopped

Create ./dnscrypt-proxy/dnscrypt-proxy.toml to specify encrypted upstream resolvers and force DNSSEC validation:

listen_addresses = ['0.0.0.0:53']

server_names = ['cloudflare', 'quad9-doh-ip4-filter-pri', 'google']

require_dnssec = true
require_nolog = true
require_nofilter = true

log_level = 2

This configuration routes all permitted queries through DNS-over-HTTPS to privacy-focused resolvers while stripping out any providers that log queries or lack DNSSEC support.

3. Populate Blocklists from Curated Sources

Access the Pi-hole web interface at http://<your-server-ip>/admin and navigate to Group Management → Adlists. Import high-quality blocklists referenced in README.md lines 499-511:

https://raw.githubusercontent.com/StevenBlack/hosts/master/hosts
https://v.firebog.net/hosts/Easyprivacy.txt
https://v.firebog.net/hosts/Prigent-Crypto.txt

Update gravity (Pi-hole's blocklist compiler) via the web interface or command line to activate the new filters.

4. Optional Hardening with Unbound for DNSSEC

For additional security against DNS cache poisoning, insert Unbound between Pi-hole and dnscrypt-proxy. The the-book-of-secret-knowledge repository references Unbound tutorials at line 1524 for this exact use case.

Add to docker-compose.yml:

  unbound:
    image: mvance/unbound:latest
    container_name: unbound
    ports:
      - "5354:53/tcp"
      - "5354:53/udp"
    volumes:
      - "./unbound/unbound.conf:/etc/unbound/unbound.conf"
    restart: unless-stopped

Configure ./unbound/unbound.conf with DNSSEC validation enabled:

server:
    interface: 0.0.0.0
    access-control: 0.0.0.0/0 allow
    verbosity: 1
    
    do-ip4: yes
    do-udp: yes
    do-tcp: yes
    
    prefetch: yes
    prefetch-key: yes
    
    harden-algo-downgrade: yes
    harden-glue: yes
    harden-dnssec-stripped: yes
    aggressive-nsec: yes
    
    val-clean-additional: yes
    val-permissive-mode: no

Modify Pi-hole's upstream DNS settings to point to 127.0.0.1#5354 instead of port 5353, then configure Unbound to forward to dnscrypt-proxy on port 5353.

Summary

• Pi-hole serves as the network's DNS authority and sinkhole engine, returning null routes for blocked domains as documented in trimstray/the-book-of-secret-knowledge line 759.
• dnscrypt-proxy encrypts all permitted queries using DNS-over-HTTPS, preventing surveillance of your DNS traffic (line 220 reference).
• Unbound optionally adds DNSSEC validation to cryptographically verify DNS responses and prevent cache poisoning (line 1524 reference).
• Community blocklists (lines 499-511) provide the threat intelligence that determines which domains get sinkholed.
• This layered architecture ensures that malware, tracking, and advertising domains never resolve on your network while maintaining privacy for legitimate DNS traffic.

Frequently Asked Questions

What is a DNS sinkhole and how does it protect my network?

A DNS sinkhole is a DNS server that intentionally gives false or null responses for specific domain queries, preventing devices from connecting to malicious or unwanted hosts. By configuring your network to use a sinkhole as its primary DNS resolver, you block threats at the resolution stage—before any TCP connection is established—effectively neutralizing command-and-control callbacks, malware downloads, and tracking pixels.

Why should I use dnscrypt-proxy instead of standard DNS upstreams?

Standard DNS queries transmit domain names in plaintext, allowing ISPs, network administrators, or attackers to monitor your browsing habits and potentially hijack responses. dnscrypt-proxy encrypts these queries using DNS-over-HTTPS (DoH) or DNS-over-TLS (DoT), ensuring that even if a domain isn't blocked by Pi-hole, the fact that you're querying it remains private from network eavesdroppers.

Can I run this DNS sinkhole setup on a Raspberry Pi?

Yes, this architecture is specifically designed for low-power devices. Pi-hole originated as a Raspberry Pi project, and both dnscrypt-proxy and Unbound have ARM-compatible Docker images. A Raspberry Pi 4 or Pi Zero 2 W can handle DNS resolution for hundreds of devices with minimal latency, though you should use high-quality SD cards or USB storage for the persistent volumes to prevent corruption from frequent database writes.

How do I automatically update blocklists in Pi-hole?

Pi-hole includes a built-in scheduler (cron) that runs pihole updateGravity weekly to refresh blocklists. You can verify or modify this schedule in /etc/cron.d/pihole inside the container, or set the SKIP_GRAVITY_ON_BOOT environment variable to false to ensure fresh lists on container restart. For immediate updates, execute docker exec pihole pihole updateGravity on your host system.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}