Firewall Performance & Traffic Load

TL;DR

Yes, firewalls can be affected by the traffic they process. High volumes of traffic, malicious attacks, or complex rule sets can all slow down a firewall and potentially cause it to fail. Monitoring performance, optimising rules, and using appropriate hardware are key to preventing issues.

How Traffic Affects Firewalls

Firewalls aren’t just passive gatekeepers; they actively inspect every packet of data that passes through them. This inspection takes processing power and memory. Here’s how traffic can cause problems:

1. CPU Overload: Each connection requires the firewall to check source/destination addresses, ports, protocols, and security rules. A large number of connections quickly consumes CPU resources.
2. Memory Exhaustion: Firewalls store information about active connections (state tables). Too many simultaneous connections can fill up memory.
3. Throughput Limits: Every firewall has a maximum amount of data it can process per second. Exceeding this limit causes packet loss and slowdowns.
4. Complex Rule Sets: The more rules you have, the longer it takes to evaluate each packet. Complex rules (e.g., using regular expressions) are particularly resource-intensive.
5. Malicious Attacks: DDoS attacks specifically aim to overwhelm a firewall with traffic, making it unavailable. Other attacks can exploit vulnerabilities and consume resources.

Signs Your Firewall is Struggling

• Slow Network Speeds: Noticeably slower internet or internal network performance.
• Packet Loss: Data packets being dropped, leading to connection issues.
• High CPU Usage: The firewall’s processor constantly running at or near 100%. You can usually check this in the firewall’s web interface or command line.
• Memory Errors: Firewall logging errors related to memory allocation.
• Connection Failures: Inability to connect to certain services or websites.

How to Prevent Firewall Issues

1. Monitor Performance: Regularly check your firewall’s CPU usage, memory consumption, and throughput. Most firewalls provide monitoring tools in their web interface. For example, on a Cisco ASA you might use the show cpu utilization command:

   show cpu utilization

2. Optimise Rules:
   • Remove unused rules.
   • Combine similar rules where possible.
   • Order rules logically – put the most frequently matched rules at the top.
   • Avoid overly complex rules if simpler ones will suffice.
3. Hardware Considerations:
   • Choose a firewall with sufficient processing power and memory for your network’s needs.
   • Consider upgrading to a more powerful firewall as your network grows.
4. Traffic Shaping & QoS: Prioritise important traffic (e.g., VoIP, video conferencing) over less critical traffic.
   Many firewalls have Quality of Service (QoS) features for this purpose.
5. Intrusion Prevention System (IPS): An IPS can detect and block malicious attacks before they overwhelm the firewall.
6. Regular Updates: Keep your firewall’s firmware and security definitions up to date to protect against new vulnerabilities.
   Check your vendor’s website for updates.
7. Load Balancing (for larger networks): Distribute traffic across multiple firewalls to prevent any single device from being overloaded.

Cyber security Best Practices

Remember that a firewall is just one part of a comprehensive cyber security strategy. You also need strong passwords, regular backups, employee training, and other security measures.