Firewall Configuration
(optional) Secure the server with firewall rules (iptables)¶
If you are behind a NAT and not running the Pi-hole on a cloud server, you do not need to issue the IPTABLES commands below as the firewall rules are already handled by the RoadWarrior installer, but you will need to portforward whatever port you chose in the setup from your public ip to your device using your router.
This step is optional but recommended if you are running your server in the cloud, such as a droplet made on Digital Ocean. If this is the case, you need to secure the server for your safety as well as others to prevent aiding in DDoS attacks.
In addition to the risk of being an open resolver, your Web interface is also open to the world increasing the risk. So you will want to prevent ports 53 and 80, respectively, from being accessible from the public Internet.
It's recommended that you clear out your entire firewall so you have full control over its setup. You have two options for setting up your firewall with your VPN.
Option 1: Allow everything from within your VPN¶
Enter this command, which will allow all traffic through the VPN tun0 interface.
iptables -I INPUT -i tun0 -j ACCEPT
Option 2: Explicitly allow what can be accessed within the VPN¶
These commands will allow DNS and HTTP needed for name resolution (using Pi-hole as a resolver) and accessing the Web interface, respectively.
iptables -A INPUT -i tun0 -p tcp --destination-port 53 -j ACCEPT
iptables -A INPUT -i tun0 -p udp --destination-port 53 -j ACCEPT
iptables -A INPUT -i tun0 -p tcp --destination-port 80 -j ACCEPT
You will also want to enable SSH and VPN access from anywhere.
iptables -A INPUT -p tcp --destination-port 22 -j ACCEPT
iptables -A INPUT -p tcp --destination-port 1194 -j ACCEPT
iptables -A INPUT -p udp --destination-port 1194 -j ACCEPT
The next crucial setting is to explicitly allow TCP/IP to do "three-way handshakes":
iptables -I INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
Also, we want to allow any loopback traffic, i.e. the server is allowed to talk to itself without any limitations using 127.0.0.0/8:
iptables -I INPUT -i lo -j ACCEPT
Finally, reject access from anywhere else (i.e. if no rule has matched up to this point):
iptables -P INPUT DROP
Blocking HTTPS advertisement assets¶
Since you're :head-desk:ing with iptables, you can also use this opportunity to block HTTPS advertisements to improve blocking ads that are loaded via HTTPS and also deal with QUIC.
Why doesn't Pi-hole just use a certificate to prevent this? The answer is here.
iptables -A INPUT -p udp --dport 80 -j REJECT --reject-with icmp-port-unreachable
iptables -A INPUT -p tcp --dport 443 -j REJECT --reject-with tcp-reset
iptables -A INPUT -p udp --dport 443 -j REJECT --reject-with icmp-port-unreachable
Depending on the systems you have connecting, you may benefit from appending --reject-with tcp-reset to the command above. If you still get slow load times of HTTPS assets, the above may help.
IPv6 iptables¶
If your server is reachable via IPv6, you'll need to run the same commands but using ip6tables:
ip6tables -A INPUT -i tun0 -p tcp --destination-port 53 -j ACCEPT
ip6tables -A INPUT -i tun0 -p udp --destination-port 53 -j ACCEPT
ip6tables -A INPUT -i tun0 -p tcp --destination-port 80 -j ACCEPT
ip6tables -A INPUT -p tcp --destination-port 22 -j ACCEPT
ip6tables -A INPUT -p tcp --destination-port 1194 -j ACCEPT
ip6tables -A INPUT -p udp --destination-port 1194 -j ACCEPT
ip6tables -I INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
ip6tables -I INPUT -i lo -j ACCEPT
ip6tables -A INPUT -p udp --dport 80 -j REJECT --reject-with icmp6-port-unreachable
ip6tables -A INPUT -p tcp --dport 443 -j REJECT --reject-with tcp-reset
ip6tables -A INPUT -p udp --dport 443 -j REJECT --reject-with icmp6-port-unreachable
ip6tables -P INPUT DROP
View the rules you just created
iptables -L --line-numbers
and they should look something like this:
Chain INPUT (policy DROP)
num target prot opt source destination
1 ACCEPT all -- anywhere anywhere
2 ACCEPT all -- anywhere anywhere state RELATED,ESTABLISHED
3 ACCEPT all -- anywhere anywhere
4 ACCEPT tcp -- anywhere anywhere tcp dpt:domain
5 ACCEPT udp -- anywhere anywhere udp dpt:domain
6 ACCEPT tcp -- anywhere anywhere tcp dpt:http
7 ACCEPT udp -- anywhere anywhere udp dpt:80
8 ACCEPT tcp -- anywhere anywhere tcp dpt:ssh
9 ACCEPT tcp -- anywhere anywhere tcp dpt:openvpn
10 ACCEPT udp -- anywhere anywhere udp dpt:openvpn
11 ACCEPT tcp -- 10.8.0.0/24 anywhere tcp dpt:domain
12 ACCEPT udp -- 10.8.0.0/24 anywhere udp dpt:domain
13 ACCEPT tcp -- 10.8.0.0/24 anywhere tcp dpt:http
14 ACCEPT udp -- 10.8.0.0/24 anywhere udp dpt:80
15 ACCEPT tcp -- 10.8.0.0/24 anywhere tcp dpt:domain
16 ACCEPT tcp -- 10.8.0.0/24 anywhere tcp dpt:http
17 ACCEPT udp -- 10.8.0.0/24 anywhere udp dpt:domain
18 ACCEPT udp -- 10.8.0.0/24 anywhere udp dpt:80
19 REJECT tcp -- anywhere anywhere tcp dpt:https reject-with icmp-port-unreachable
Chain FORWARD (policy ACCEPT)
num target prot opt source destination
Chain OUTPUT (policy ACCEPT)
num target prot opt source destination
Similarly, ip6tables -L --line-numbers should look like this:
Chain INPUT (policy DROP)
num target prot opt source destination
1 ACCEPT all anywhere anywhere
2 ACCEPT all anywhere anywhere state RELATED,ESTABLISHED
3 ACCEPT tcp anywhere anywhere tcp dpt:domain
4 ACCEPT udp anywhere anywhere udp dpt:domain
5 ACCEPT tcp anywhere anywhere tcp dpt:http
6 ACCEPT udp anywhere anywhere udp dpt:80
7 ACCEPT tcp anywhere anywhere tcp dpt:ssh
8 ACCEPT tcp anywhere anywhere tcp dpt:openvpn
9 ACCEPT udp anywhere anywhere udp dpt:openvpn
10 REJECT tcp anywhere anywhere tcp dpt:https reject-with icmp6-port-unreachable
Chain FORWARD (policy ACCEPT)
num target prot opt source destination
Chain OUTPUT (policy ACCEPT)
num target prot opt source destination
Verify the rules are working¶
Connect to the VPN as a client and verify you can resolve DNS names as well as access the Pi-hole Web interface. These settings are stored in memory until you save them. If it's not working, you can restart your server to start from scratch. Alternatively, you could also go through and delete lines with iptables -D INPUT <SOME LINE NUMBER>
Save your iptables¶
If things look good, you may want to save your rules so you can revert to them if you ever make changes to the firewall. Save them with these commands:
iptables-save > /etc/pihole/rules.v4
ip6tables-save > /etc/pihole/rules.v6
Similarly, you can restore these rules:
iptables-restore < /etc/pihole/rules.v4
ip6tables-restore < /etc/pihole/rules.v6