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iptables config
Now it's time to set up a firewall to limit and block unwanted inbound traffic to your Pi. This step is optional, it is strongly recommend that you use the example below to block traffic to ports that are not commonly used. It's a good way to deter would-be intruders! You can always modify the rules or disable the firewall later.
Here's how to create a firewall on your Pi:
Check your Pi's default firewall rules by entering the following command:
sudo iptables -L
Examine the output. If you haven't implemented any firewall rules yet, you should see an empty ruleset, as shown below:
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
Create a file to hold your firewall rules by entering the following command:
sudo nano /etc/iptables.firewall.rules
Now it's time to create some firewall rules. We've created some basic rules to get you started. Copy and paste the rules shown below in to the iptables.firewall.rules file you just created.
*filter
# by default drop input
-P INPUT DROP
# Allow all loopback (lo0) traffic and drop all traffic to 127/8 that doesn't use lo0
-A INPUT -i lo -j ACCEPT
-A INPUT -d 127.0.0.0/8 -j REJECT
# Accept all established inbound connections
-A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
# Allow all outbound traffic - you can modify this to only allow certain traffic
-A OUTPUT -j ACCEPT
# Allow HTTP and HTTPS connections from anywhere (the normal ports for websites and SSL).
-A INPUT -p tcp --dport 80 -j ACCEPT
-A INPUT -p tcp --dport 443 -j ACCEPT
# Allow HTTP/HTTPS connection from anywhere to Gekko app
-A INPUT -p tcp -s 192.168.0.0/16 --dport 3000 -j ACCEPT
# Allows SMTP access
#-A INPUT -p tcp --dport 25 -j ACCEPT
#-A INPUT -p tcp --dport 465 -j ACCEPT
#-A INPUT -p tcp --dport 587 -j ACCEPT
# Allows pop and pops connections
# -A INPUT -p tcp --dport 110 -j ACCEPT
# -A INPUT -p tcp --dport 995 -j ACCEPT
# Allows imap and imaps connections
#-A INPUT -p tcp --dport 143 -j ACCEPT
#-A INPUT -p tcp --dport 993 -j ACCEPT
# Allow SSH connections
# The -dport number should be the same port number you set in sshd_config
-A INPUT -p tcp -m state --state NEW --dport 1707 -j ACCEPT
# Allow ping
-A INPUT -p icmp --icmp-type echo-request -j ACCEPT
# Log iptables denied calls
-A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7
# Drop all other inbound - default deny unless explicitly allowed policy
#-A INPUT -j DROP
-A FORWARD -j DROP
COMMIT
Edit the rules as necessary. By default, the rules will allow traffic to the following services and ports:
- HTTP (80)
- HTTPS (443)
- SSH (1707)
- ping (ICMP)
I also added commented out SMTP, Pop and IMAP in case you need. All other ports will be blocked.
Save the changes to the firewall rules file by pressing Control-X, and then Y. Activate the firewall rules by entering the following command:
sudo iptables-restore < /etc/iptables.firewall.rules
Recheck your Pi's firewall rules by entering the following command:
sudo iptables -L
Examine the output. The new ruleset should look like the one shown below:
Chain INPUT (policy DROP)
target prot opt source destination
ACCEPT all -- anywhere anywhere
REJECT all -- anywhere loopback/8 reject-with icmp-port-unreachable
ACCEPT all -- anywhere anywhere state RELATED,ESTABLISHED
ACCEPT tcp -- anywhere anywhere tcp dpt:http
ACCEPT tcp -- anywhere anywhere tcp dpt:https
ACCEPT tcp -- anywhere anywhere tcp dpt:3000
ACCEPT tcp -- anywhere anywhere state NEW tcp dpt:1707
ACCEPT icmp -- anywhere anywhere icmp echo-request
LOG all -- anywhere anywhere limit: avg 5/min burst 5 LOG level debug prefix "iptables denied: "
Chain FORWARD (policy ACCEPT)
target prot opt source destination
DROP all -- anywhere anywhere
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
ACCEPT all -- anywhere anywhere
Now you need to ensure that the firewall rules are activated every time you restart your Pi. Start by creating a new script with the following command:
sudo nano /etc/network/if-pre-up.d/firewall
Copy and paste the following lines in to the file you just created: #!/bin/sh /sbin/iptables-restore < /etc/iptables.firewall.rules
Press Control-X and then press Y to save the script. Set the script's permissions by entering the following command:
sudo chmod +x /etc/network/if-pre-up.d/firewall
That's it! Your firewall rules are in place and protecting your Pi. Remember, you'll need to edit the firewall rules later if you install other software or services.