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Firewall troubleshooting steps & solutions to common issues


Problems with firewalls can be quite disastrous to your operations. When firewall rules are not set properly, you might deny all requests, even valid ones, or allow access to unauthorized sources.

There needs to be a systematic way to troubleshoot your firewall issues, and you need to have a proper plan.

You should consider security standards, hardware/software compatibility, security policy planning, and access level specifications.

It is recommended to have an ACL (access control list) to determine who has access to what.

Let us give you a brief overview of firewall troubleshooting best practices and steps to follow.

Common firewall problems

With the many benefits that firewalls bring, they might also pop out some errors and issues now and then. You need to be aware of the common issues, failures, and error codes to properly assess an error condition to ensure the smooth working of your firewalls.

Misconfiguration errors

A report by Gartner Research says that misconfiguration causes about 95% of all firewall breaches. A simple logical flaw in a firewall rule can open up vulnerabilities, leading to serious security breaches.

Before playing with your firewall settings, you must set up proper access control settings and understand the security policy specifications. You must remember that misconfiguration errors in CLI can lead to hefty fines for non-compliance, data breaches, and unnecessary downtimes.

All these can cause heavy monetary damages; hence, you should take extra care to configure your firewall rules and settings properly.

Here are some common firewall misconfigurations:

  • Allowing ICMP and making the firewall available for ping requests
  • Providing unnecessary services on the firewall
  • Allowing unused TCP/UDP ports
  • The firewall is set to return a ‘deny’ response instead of a ‘drop’ for blocked ports.
  • IP address misconfigurations that can allow TCP pinging of internal hosts from external devices.
  • Trusting DNS and IP addresses that are not properly checked and source verified.

Check out AlgoSec’s firewall configuration guide for best practices.

Hardware issues

Hardware bottlenecks and device misconfigurations can easily lead to firewall failures.

Sometimes, running a firewall 24/7 can overload your hardware and lead to a lowered network performance of your entire system.

You should look into the performance issues and optimize firewall functionalities or upgrade your hardware accordingly.

Software vulnerabilities

Any known vulnerability with your firewall software must be dealt with immediately. Hackers can exploit software vulnerabilities easily to gain backdoor entry into your network. So, stay current with all the patches and updates your software vendors provide.

Speak to one of our experts

Types of firewall issues

Most firewall issues can be classified as either connectivity or performance issues. Here are some tools you can use in each of these cases:

Connectivity Issues

Some loss of access to a network resource or unavailability usually characterizes these issues. You can use network connectivity tools like NetStat to monitor and analyze the inbound TCP/UDP packets. Both these tools have a wide range of sub-commands and tools that help you trace IP network traffic and control the traffic as per your requirements.

Firewall Performance Issues

As discussed earlier, performance issues can cause a wide range of issues, such as unplanned downtimes and firewall failures, leading to security breaches and slow network performance. Some of the ways you can rectify it include:

  • Load balancing by regulating the outbound network traffic by limiting the internal server errors and streamlining the network traffic.
  • Filtering the incoming network traffic with the help of Standard Access Control List filters.
  • Simplifying firewall rules to reduce the load on the firewall applications. You can remove unused rules and break down complex rules to improve performance.

Firewall troubleshooting checklist steps

Step 1. Audit your hardware & software

Create a firewall troubleshooting checklist to check your firewall rules, software vulnerabilities, hardware settings, and more based on your operating system. This should include all the items you should cover as part of your security policy and network assessment.

With Algosec’s policy management, you can ensure that your security policy is complete, comprehensive and does not miss out on anything important.

Step 2. Pinpoint the Issue

Check what the exact issue is. Generally, a firewall issue can arise from any of the three conditions:

  • Access from external networks/devices to protected resources is not functioning properly
  • Access from the protected network/resources to unprotected resources is not functioning properly.
  • Access to the firewall is not functioning properly.

Step 3. Determine the traffic flow

Once you have ascertained the exact access issue, you should check whether the issue is raised when traffic is going to the firewall or through the firewall. Once you have narrowed down this issue, you can test the connectivity accordingly and determine the underlying cause.

  • Check for any recent updates and try to roll back if that can solve the issue.
  • Go through your firewall permissions and logs for any error messages or warnings.
  • Review your firewall rules and configurations and adjust them for proper working.
  • Depending upon your firewall installation, you can make a checklist of items. Here is a simple guide you can follow to conduct routine maintenance troubleshooting.
  • Monitor the network, test it out, and repeat the process until you reach a solution.

Firewall troubleshooting best practices

Here are some proven firewall troubleshooting tips. For more in-depth information, check out our Network Security FAQs page.

Monitor and test

Regular auditing and testing of your Microsoft firewall can help you catch vulnerabilities early and ensure good performance throughout the year. You can use expert-assisted penetration testing to get a good idea of the efficacy of your firewalls.

Also be sure to check out the auditing services from Algosec, especially for your PCI security compliance.

Deal with insider threats

While a Mac or Windows firewall can help you block external threats to an extent, it can be powerless regarding insider attacks. Make sure you enforce strong security controls to avoid any such conditions.

Your security policies must be crafted well to avoid any room for such conditions, and your access level specifications should also be well-defined.

Device connections

Make sure to pay attention to the other modes of attack that can happen besides a network access attempt. If an infected device such as a USB, router, hard drive, or laptop is directly connected to your system, your network firewall can do little to prevent the attack.

So, you should put the necessary device restrictions in your privacy statement and the firewall rules.

Review and Improve

Update your firewall rules and security policies with regular audits and tests. Here are some more tips you can follow to improve your firewall security:

  • Optimize your firewall ruleset to allow only necessary access
  • Use unique user IP instead of a root ID to launch the firewall services
  • Make use of a protected remote Syslog server and keep it safe from unauthorized access
  • Analyze your firewall logs regularly to identify and detect any suspicious activity. You can use tools like Algosec Firewall Analyzer and expert help to analyze your firewall as well.
  • Disable FTP connections by default
  • Setup strict controls on how and which users can modify firewall configurations.
  • Include both source and destination IP addresses and the ports in your firewall rules.
  • Document all the updates and changes made to your firewall policies and rules.
  • In the case of physical firewall implementations, restrict the physical access as well.
  • Use NAT (network address translation) to map multiple private addresses to a public IP address before transmitting the information online.

How does a firewall actually work?

A Windows firewall is a network security mechanism that allows you to restrict incoming network traffic to your systems.

It can be implemented as a hardware, software, or cloud-based security solution. It acts as a barrier stopping unauthorized network access requests from reaching your internal network and thus minimizing any attempt at hacking or breach of confidential data.

Based on the type of implementation and the systems it is protecting, firewalls can be classified into several different types. Some of the common types of firewalls are:

  • Packet filtering – Based on the filter standards, a small amount of incoming data is analyzed and subjected to restriction on distribution across the network.
  • Proxy service – An application layer service that acts as an intermediary between the actual servers to block out unauthorized access requests.
  • Stateful inspection – A dynamic packet filtering mechanism that filters out the network packets.
  • Next-Generation Firewall (NGFW) –  A combination of deep packet inspection and application level inspection to block out unauthorized access into the network.

Firewalls are essential to network security at all endpoints, whether personal computers or full-scale enterprise data centers. They allow you to set up strong security controls to prevent a wide range of cyberattacks and help you gain valuable data.

Firewalls can help you detect suspicious activities and prevent intrusive attacks at the earliest. They can also help you regulate your incoming and outgoing traffic routing, helping you implement zero-trust security policies and stay compliant with security and data standards.


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