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Secure Pi-hole & UniFi "Chained DNS" Configuration

This guide details the optimal topology for running Pi-hole in a container alongside a UniFi Router (UDM/USG). This setup ensures ad-blocking, local hostname resolution, and maximum security by preventing DNS bypass.

The Topology: Chained DNS

In this setup, Pi-hole is the only DNS server the clients know about. However, Pi-hole uses the UniFi Router as its upstream provider. This keeps the router "in the loop" for local device naming and security filtering.

flowchart LR
    %% Nodes
    Clients["Network Clients
(Laptops, IoT, Phones)"]
    PiHole[("Pi-hole Container
(Ad Blocking)")]
    UniFi[("UniFi Gateway
(Local Names & GeoIP)")]
    Upstream["Secure Upstream DNS
(Quad9 / Cloudflare)"]
    Blocked[("Blocked Domains
(Ads/Trackers)")]

    %% Styles
    style PiHole fill:#f9f,stroke:#333,stroke-width:2px
    style UniFi fill:#bbf,stroke:#333,stroke-width:2px
    style Blocked fill:#ff9999,stroke:#333

    %% Connections
    Clients -->|"DNS Query (Port 53)"| PiHole
    PiHole -->|"Blocked?"| Blocked
    PiHole -->|"Allowed?"| UniFi
    UniFi -->|"Resolve External"| Upstream

    %% Firewall Logic
    subgraph LAN_Security ["UniFi Firewall Rules"]
    direction TB
    Rule1["Allow: Pi-hole to Internet:53"]
    Rule2["Block: All Clients to Internet:53"]
    end

Implementation Steps

1. Configure UniFi DHCP (LAN Settings)

Force all network clients to use Pi-hole exclusively.

  • Navigate to: UniFi Network → Settings → Networks → [Your LAN].
  • DHCP Service Management:
  • DHCP DNS Server: Uncheck "Auto".
  • DNS Server 1: Enter [Pi-hole IP Address].
  • DNS Server 2: Leave BLANK.
  • Note: Do not add a secondary public DNS (like 8.8.8.8), or devices will bypass ad-blocking.

2. Configure Pi-hole Upstream

Tell Pi-hole to ask the UniFi router for help. This ensures local hostnames (like printer.local) resolve correctly.

  • Navigate to: Pi-hole Admin → Settings → DNS.

  • Upstream DNS Servers:

  • Uncheck all pre-set public providers (Google, OpenDNS, etc.).

  • Custom 1 (IPv4): Enter [UniFi Gateway IP] (usually 192.168.1.1).

  • Advanced Settings:

  • Enable: "Never forward non-FQDNs".

  • Enable: "Never forward reverse lookups for private IP ranges".

3. Configure UniFi WAN (Internet Settings)

Define where the router ultimately sends traffic.

  • Navigate to: UniFi Network → Settings → Internet → WAN.
  • DNS Server: Uncheck "Auto".
  • Primary Server: 9.9.9.9 (Quad9 - recommended for security) or 1.1.1.2 (Cloudflare - malware blocking).
  • Note: This allows the UniFi security features (Country Blocking/DNS Shield) to apply to the final outbound request.

Security: Preventing Bypass (Port 53 Redirection)

Smart devices (e.g., Chromecasts, Roku) often ignore DHCP settings and try to use Google DNS (8.8.8.8) directly. You must block this using UniFi Firewall rules.

Create the following rules in Settings → Security → Traffic Rules (or Firewall):

  1. Rule Name: Allow Pi-hole DNS
  • Action: Allow
  • Source: [Pi-hole IP Address]
  • Destination: Port 53 (Any)
  1. Rule Name: Block Direct DNS
  • Action: Block
  • Source: All Local Networks (LAN/IoT/VLANs)
  • Destination: Port 53
  • Note: Since the Pi-hole is allowed in Rule 1, this blocks everyone ELSE.