10 pfSense Firewall Rules Best Practices

pfSense is a free and open source firewall and router that is widely used in the enterprise. It has a wide range of features and can be configured to suit any network environment.

One of the most important aspects of configuring pfSense is creating firewall rules. Firewall rules define what traffic is allowed into and out of the network. They are the first line of defense against attacks and can help prevent sensitive data from being leaked.

In this article, we will discuss 10 best practices for creating firewall rules in pfSense. By following these best practices, you can ensure that your pfSense firewall is properly configured to protect your network.

1. Use the most specific rule possible

If you have a rule that allows all traffic from a specific IP address, and then another rule that blocks all traffic from that same IP address, the second rule will never be reached. This is because the first rule will always match and allow the traffic, so the second rule will never even be checked.

To avoid this issue, make sure to use the most specific rule possible. In the example above, the rule blocking traffic from the specific IP address should come before the rule allowing all traffic from that IP address. That way, the blocking rule will be checked first, and only traffic that isn’t explicitly allowed will be blocked.

2. Put more specific rules before less specific ones

When the pfSense firewall is processing traffic, it goes through each rule one at a time in the order that they are listed. So if you have a rule that allows all traffic from a specific IP address, and then a rule that blocks all traffic from another IP address, the first rule is going to take precedence.

This might not seem like a big deal, but it can cause some serious problems if you’re not careful. For example, let’s say you have a rule that allows all traffic from your office IP address range, and then a rule that blocks all traffic from a specific malicious IP address.

If you put the rule for your office IP address range first, then the rule for the malicious IP address will never be reached. This means that the malicious traffic will be allowed through, even though you were trying to block it.

To avoid this problem, always put more specific rules before less specific ones. In the example above, you would want to put the rule for the malicious IP address first, so that it takes precedence over the rule for your office IP address range.

3. Block traffic by default

If you don’t block traffic by default, any new traffic that arrives on your network will be allowed unless you have a rule specifically blocking it. This can be a major security risk since it’s easy to overlook new traffic types.

By contrast, if you block all traffic by default, you know that any traffic that is allowed is explicitly allowed by a rule. This makes it much easier to spot potential security risks since you can quickly see which traffic is allowed and which isn’t.

Of course, this doesn’t mean that you should never allow any traffic. You’ll still need to create rules to allow the traffic you want. But blocking traffic by default is a good starting point for creating a secure firewall configuration.

4. Allow only what is needed

By only allowing what is needed, you are essentially locking down your network so that only authorized traffic can flow through. This helps to prevent unauthorized access and also helps to improve performance by reducing the amount of traffic that needs to be processed.

To implement this best practice, you will need to create firewall rules that allow only the specific traffic that you want to allow. For example, if you only want to allow HTTP traffic, you would create a rule that allows only traffic from port 80. By doing this, you are ensuring that only the traffic that you want to allow is able to pass through your firewall.

5. Be consistent with your firewall policy

If you’re not consistent with your firewall policy, it will be difficult to troubleshoot issues that may arise. For example, if you allow traffic from one subnet but block it from another, it can be difficult to determine why the traffic is being blocked.

It’s also important to be consistent with your rule naming convention. This will make it easier to remember what each rule does, and it will also make it easier to search for specific rules.

Finally, it’s a good idea to document your firewall rules. This documentation can be in the form of comments within the rules themselves, or it can be in a separate document. Either way, it’s important to have a record of what your firewall rules are and why they’re in place.

6. Avoid using aliases in firewall rules

When you add an alias to a firewall rule, pfSense will automatically update the rule when the IP address or range of addresses in the alias changes. This can be handy in some situations, but it can also cause problems if the IP addresses in the alias change frequently or without your knowledge.

For example, let’s say you have a rule that allows traffic from a specific IP address to access your web server. You add the IP address to an alias so that you can easily update the rule if the IP address changes.

However, what happens if the IP address in the alias changes without you knowing? Your firewall rule will now allow traffic from a different IP address than you intended, which could potentially be harmful.

To avoid this problem, don’t use aliases in firewall rules. Instead, add the specific IP addresses or ranges of addresses that you want to allow or block to the rule itself. That way, you’ll always know exactly which IP addresses are being allowed or blocked by the rule.

7. Minimize the number of firewall rules

The more firewall rules you have, the more complex your rule set becomes. This can make it difficult to troubleshoot issues and can also lead to security vulnerabilities.

It’s important to remember that each rule has the potential to introduce a security vulnerability. Therefore, it’s crucial to only create firewall rules for the services and applications that you absolutely need.

Additionally, you should review your firewall rules on a regular basis to ensure that they are still relevant and that there haven’t been any changes to the services or applications that you are using.

8. Keep a log of all changes to the firewall configuration

If you ever need to troubleshoot an issue or roll back a change, having a log will make it much easier to find the cause of the problem and fix it. Additionally, if you have multiple people working on the firewall, a log can help prevent accidental changes from being made.

To enable logging in pfSense, go to Status > System Logs and click the Settings tab. Then, check the boxes next to the types of logs you want to keep track of.

9. Test your firewall rules

When you make a change to your firewall, there’s always the potential to break something. By testing your changes before you deploy them, you can be sure that they work as intended and that you’re not accidentally blocking traffic that you need.

There are a few different ways to test your firewall rules. One is to use a tool like pfSense Test Center, which will allow you to simulate traffic and see how your firewall handles it.

Another option is to use a tool like WireShark to capture live traffic and then analyze it to see what’s being blocked and what’s getting through.

Either way, testing your firewall rules is an essential best practice to ensure that your changes don’t break anything.

10. Monitor your firewall logs

Your firewall is constantly being bombarded with traffic, both good and bad. By default, pfSense will log all this activity, which can be useful for troubleshooting purposes. However, if you’re not regularly monitoring these logs, you could be missing important information about attacks on your network.

There are a few different ways to monitor your firewall logs. The easiest way is to use the built-in Log Viewer in the pfSense web interface. This will give you a real-time view of all the activity passing through your firewall.

If you want more comprehensive logging, you can enable syslogging and send your logs to a central syslog server. This is a bit more complex to set up, but it’s worth it for the added security.

Finally, you can also use a third-party logging tool like Splunk or Graylog. These tools will provide you with even more detailed information about the traffic passing through your firewall.