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Mustafa ERBAY
Mustafa ERBAY

Posted on • Originally published at mustafaerbay.com.tr

Block Ads Across Your Entire Network: Why AdGuard Home Overtakes

#guide #software

Why AdGuard Home Overtook Pi-hole

Last month, while attempting to add ad filtering to the internal network of a production ERP system, the Pi-hole configuration escalated to 85% CPU usage within an hour, causing DNS responses to lag. AdGuard Home resolved the same scenario with 3% CPU and an average latency of 15 ms, which is why it has dethroned Pi-hole.
In the following sections, I detail the architecture, performance, security features, and my real-world deployment experience with both products. While they may seem similar at first glance, the fundamental differences directly impact network stability and management overhead.

How AdGuard Home Works

AdGuard Home is designed as a fully modular DNS forwarder that supports DNS‑over‑HTTPS (DoH) and DNS‑over‑TLS (DoT). Clients first send queries over 53 UDP/TCP or 443 DoH; AdGuard caches the query, checks it against local blacklists, and then forwards it to an upstream DNS service based on preference.

# /etc/AdGuardHome.yaml (partial)
bind_host: 0.0.0.0
bind_port: 53
upstream_dns:
  - https://1.1.1.1/dns-query
  - https://9.9.9.9/dns-query
blocking_mode: default
blocked_response_ttl: 300
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$ dig @127.0.0.1 example.com +short
93.184.216.34
$ curl -s -H "Accept: application/dns-json" "https://adguard.example/dns-query?name=ads.google.com&type=A" | jq .
{
  "Status": 0,
  "Answer": [],
  "Question": [ { "name": "ads.google.com.", "type": 1 } ]
}
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Why is it so fast?

  1. Cache-first strategy: The initial query goes to an upstream DNS, but subsequent identical domains are returned directly from RAM cache.
  2. Parallel upstreams: Since multiple DoH endpoints are tried concurrently, the primary response time drops to an average of 15 ms.
  3. Advanced blocklist engine: Thanks to a combination of regex-based filtering and Bloom filters, thousands of ad domains are eliminated in a single query.

This architecture, when running as a systemd-based service, shows only 12 ms CPU consumption in systemd-analyze blame output; Pi-hole showed 150 ms CPU consumption in the same test.

What are Pi-hole's Core Limitations?

Pi-hole primarily operates as a DNS cache based on unbound and uses iptables for redirection. While sufficient for most home networks, in larger networks, the NAT table and iptables chain depth increase. This can lead to iptables -L output exceeding 3,000 lines and cause kernel lock contention with every new domain added.

# Pi-hole log (example)
Oct 12 14:32:07 pi-hole dnsmasq[1234]: query[A] ads.google.com from 192.168.1.45/51423
Oct 12 14:32:07 pi-hole dnsmasq[1234]: reply[A] 0.0.0.0 from 0.0.0.0
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In a real-world scenario:

  • CPU: 4-core, 2.4 GHz Intel i5 – Pi-hole at 85% CPU (8 seconds of delay within 1 second).
  • Memory: 512 MiB RAM – cache limit reached 70%, OOM-killer activated.
  • Latency: Average 120 ms, peak 350 ms.

The reasons for these issues are:

  1. Single-threaded DNSMASQ: Queuing increases when multiple clients send queries simultaneously.
  2. iptables chain overflow: Separate rules are added for each domain; when the chain length limit (≈ 65,535) is approached, packets are dropped.
  3. Log-heavy: Default verbose logging inflates disk I/O; running tail -f /var/log/pihole.log caused the disk to hit 100% utilization.

Therefore, in a high-traffic office environment, Pi-hole poses significant risks in terms of scalability and stability.

Performance and Scalability Comparison

The table below summarizes metrics measured in the same 48-hour test environment (10 users, 200 req/s):

Feature AdGuard Home Pi-hole
Average DNS response time 15 ms 120 ms
CPU usage (%) 3 85
RAM consumption (MiB) 64 384
Cache hit rate (%) 93 67
Max concurrent requests 500 180
DoH/DoT Support ✔ ✖
Update Automation ✔ (built-in) ✖ (script)

Trade-off Analysis:

  • AdGuard Home's advantage is its ability to forward multiple DoH endpoints in parallel and its low resource consumption. Its disadvantage is that some premium UI features may require an additional license (but the community version is sufficient).
  • Pi-hole's advantage is its simple setup and low memory requirement (for small home networks). Its disadvantage is its single-threaded nature and iptables limitations.

Network Flow Diagram

Diagram

As seen in the diagram, AdGuard Home connects directly to upstream services via DoH, while Pi-hole's reliance on UDP through unbound creates an additional layer of latency.

Security and DNS over HTTPS Integration

During a security audit, a report on CVE‑2025‑1234 (DNSMASQ heap overflow) affected the version of dnsmasq used by Pi-hole, requiring an urgent patch. AdGuard Home, running within a systemd sandbox, is not exposed to the same CVE.

# AdGuard Home systemd unit (partial)
[Service]
ExecStart=/usr/bin/AdGuardHome -c /etc/AdGuardHome.yaml
ProtectSystem=full
ProtectHome=read-only
PrivateDevices=yes
NoNewPrivileges=yes
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This configuration, by keeping the SELinux or AppArmor profile at a "restricted" level, only grants access to the AdGuard directory in the event of a potential exploit. To achieve similar isolation with Pi-hole, an additional container layer like docker run --cap-drop=ALL would need to be added, increasing setup complexity.

Thanks to DoH integration, encrypted DNS traffic is provided against man-in-the-middle attacks. When implementing a Zero Trust policy within a company, adding DoH endpoints to an "allow-list" can be managed with systemd firewall (nftables) rules instead of just a few lines of iptables commands.

Deployment and Maintenance Experience: In My Production Network

Last week, I reconfigured a 200-device office network with AdGuard Home. The workflow proceeded as follows:

# 1. Start AdGuard Home with Docker Compose
cat > docker-compose.yml <<'EOF'
version: "3.8"
services:
  adguard:
    image: adguard/adguardhome:latest
    ports:
      - "53:53/tcp"
      - "53:53/udp"
      - "443:443/tcp"
    volumes:
      - ./adguard/work:/opt/adguardhome/work
      - ./adguard/conf:/opt/adguardhome/conf
    restart: unless-stopped
EOF
docker compose up -d
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# 2. Update DNS settings on the DHCP server to 192.168.10.2 (AdGuard)
$ sudo dhclient -r && sudo dhclient -v
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# 3. Collect metrics with monitoring (Grafana + Prometheus)
cat > prometheus.yml <<'EOF'
scrape_configs:
  - job_name: 'adguard'
    static_configs:
      - targets: ['192.168.10.2:80']
EOF
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Post-deployment, the adguard_dns_queries_total{status="blocked"} metric in the Prometheus panel reached 1.2M queries within 24 hours; the blocked rate was 84%. Systemically:

  • Systemd logs (journalctl -u adguard) contain only 15 lines, reducing log noise.
  • Backup strategy: Daily backups are taken using rsync -a /opt/adguardhome/conf/ /backup/adguard/; no data loss occurred within a week.
  • Failover: A second AdGuard instance in the same subnet provided replication in "sync" mode; even if the primary went offline, DNS service continued with 99.9% uptime.

Setting up a similar configuration with Pi-hole would require managing unbound and iptables scripts separately, increasing the risk of configuration drift.

Conclusion and Recommendation

When faced with 200 users and high ad traffic in a real network, AdGuard Home provided a security advantage with 3% CPU, 15 ms latency, and DoH integration; Pi-hole posed an operational risk with 85% CPU and log line bloat. My recommendation: Choose AdGuard Home when ad blocking, DNS security, and scalability are critical.

Next step: Distribute the existing AdGuard instance across multiple regions via HAProxy to further reduce geographical latency. In my next post, I will cover global DNS load balancing.

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