DNS RPZ: A DIY Firewall to Block Sites and Keep Users Safe
If you’re tired of pop‑ups, phishing attempts, or just don’t want a particular site in your browsing history, this guide shows how to turn your own DNS server into a low‑overhead blocker. By the end you’ll have a working DNS RPZ (Response Policy Zone) that stops those domains before they even hit your browser.
What Is DNS RPZ?
RPZ is a feature built into many open‑source DNS servers that lets you rewrite or refuse answers to certain queries. Think of it as a “blacklist” applied at the resolver level, so any device that asks your server for an IP gets a clean denial or a custom response instead.
Why bother? Browser extensions and hosts files are great but they sit inside the OS or app. An RPZ sits before those layers: if your DNS never gives out the address, the site can’t load at all. That’s handy when you want to block malicious sites for everyone on a network—no per‑device configuration required.
Why Use It Instead of Browser Blockers?
- Whole‑network coverage: No need to set up an extension on every laptop or phone.
- Works with DNS over HTTPS/TLS if your devices are forced to use your server (e.g., via DHCP).
- Instant, no software update required.
- No “guess the file path” headaches like messing around with /etc/hosts.
That said, RPZ won’t catch traffic that bypasses your local DNS—so if someone flips to a public resolver they’ll slip through.
Getting Started – Set Up a Local RPZ Server on Ubuntu
You only need one machine (a spare Raspberry Pi or an old PC) and about 10 GB of disk. I’ve been running it on a Pi‑3 for years; nothing fancy needed.
1. Install BIND9
sudo apt update sudo apt install bind9 bind9utils
BIND is the most mature DNS server that ships with RPZ support out of the box.
2. Create a directory for your policy zones
sudo mkdir -p /etc/bind/rpz sudo chown bind:bind /etc/bind/rpz
Keeps your policy files separate from the rest of BIND’s config, making backup easy.
3. Tell BIND to load RPZ zones
Edit /etc/bind/named.conf.options and add:
options {
...
zone-statistics yes;
rrsig-signing-key-file "/etc/bind/rpz/keyfile";
rpz-allow-same-as-master no;
};
These directives enable the policy engine and give it a place for its key.
4. Generate a signing key (optional but recommended)
sudo rndc-confgen -a -b 2048 -s /etc/bind/rpz/keyfile
RPZ can be signed, adding an extra layer of tamper‑proofing.
5. Add the RPZ zone definition
Append to /etc/bind/named.conf.local:
zone "rpz.example.net" {
type master;
file "/etc/bind/rpz/rpz.zone";
allow-query { none; };
also-notify { 127.0.0.1; };
};
This tells BIND where to look for the policy rules.
Adding Rules to Your RPZ Zone File
Create /etc/bind/rpz/rpz.zone:
$TTL 86400
@ IN SOA ns.rpz.example.net. admin.rpz.example.net. (
2024021101 ; serial
7200 ; refresh
3600 ; retry
1209600 ; expire
86400 ) ; minimum
; Default action: refuse all queries that match the policy zone
@ IN RPZ REFUSE
Now add specific domains you want to block. Each line rewrites the response:
malicious.com. IN RPZ DROP phishbank.net. IN RPZ DROP ads.example.org. IN RPZ DROP
Why each rule matters:
- DROP stops the resolver from handing out an IP at all.
- If you prefer a “soft block” (e.g., redirect to a warning page), use REPLACE with an A record pointing to that server.
After editing, reload BIND:
sudo rndc reload rpz.example.net
You should see a quick log entry confirming the zone reloaded.
Configuring Your Devices to Use the RPZ Server
1. Set your router’s DNS: Point it to 192.168.1.2 (the IP of your Pi).
Every device that asks the router for a name will now hit your RPZ server.
2. Force DNS over TLS/HTTPS (optional)
Add a line in /etc/bind/named.conf.options:
tls-cert-file "/path/to/server.pem"; tls-key-file "/path/to/key.pem";
Then configure clients to use https://192.168.1.2/dns-query.
Prevents man‑in‑the‑middle from snooping or spoofing your queries.
3. Verify: On a client, run
dig @192.168.1.2 malicious.com
The response should be REFUSED or an empty answer if you used DROP.
Common Pitfalls and Gotchas
- IPv6 leaks: If devices still use the global DNS for IPv6, add a separate RPZ zone for AAAA queries.
- Recursive queries disabled: Some routers disable recursion; make sure BIND is set to allow it (recursion yes;).
- Mis‑spelled domain names: A typo in the zone file means the site stays live. Double‑check with dig example.com.
- Caching delays: After adding a rule, clear local DNS caches (e.g., ipconfig /flushdns on Windows) to see changes immediately.
Wrap‑up
Setting up an RPZ isn’t rocket science—you just need a machine that can run BIND, a few lines of config, and the will to keep your network tidy. Once in place, you get a system‑wide firewall that blocks bad sites at the very first step: DNS resolution.
Give it a spin, tweak the rules as you discover new nuisances, and enjoy a cleaner browsing experience without any extra browser extensions.
