A firewall is a security system that monitors and controls incoming and outgoing network traffic based on rules, deciding what gets through and what gets blocked before it reaches your systems.

Firewalls have been around long enough that most people assume they know what one does. They're partly right. But there's a real gap between the general idea and what a firewall does (and doesn't do) in a modern business network, and that gap is worth closing.

The simple way to think about it

Picture every piece of data entering or leaving your network as a car driving through a checkpoint. The firewall is the guard at the gate. It checks each vehicle against a set of rules: where it's coming from, where it's going and what it's carrying. Traffic that matches the approved rules gets waved through. Traffic that doesn't gets turned away or flagged for a closer look.

Without a firewall, there's no checkpoint. Every car drives straight onto your network, and you have no view of what's coming or going.

Hardware vs. software firewalls

Firewalls come in two forms, and most well-run business networks use both.

Hardware firewalls are dedicated physical devices that sit between your internal network and the internet. All traffic entering or leaving the network passes through them first, so they protect the whole network perimeter and are managed centrally by IT. This is what NerdSquad deploys and manages for business clients. Many business firewalls can also connect to two internet providers at once; see internet failover with a dual-WAN firewall for how that keeps the office online when one connection drops.

Software firewalls run on individual devices. Windows Defender Firewall, for example, runs on every Windows PC. They control traffic at the device level, which makes them a useful second layer for catching threats that got past the perimeter or protecting a laptop that leaves the office.

You don't have to choose. A layered approach, with a hardware firewall at the perimeter and a software firewall on each device, is the standard for business networks.

What modern firewalls do

Early firewalls filtered traffic by IP address and port. Modern next-generation firewalls (NGFW) do considerably more:

• Deep packet inspection: looking inside data packets, not just at the envelope, to spot malicious content or unauthorized applications
• Application awareness: recognizing specific applications and applying rules based on which app is generating the traffic
• Intrusion detection and prevention (IDS/IPS): identifying and blocking known attack patterns as they happen
• SSL/TLS inspection: decrypting and inspecting encrypted traffic, which attackers use to hide malicious payloads
• DNS filtering: blocking connections to known malicious domains before any data is exchanged, which also stops many phishing links from loading
• Traffic logging: recording what passes through for investigations and audits, which supports HIPAA and other compliance frameworks

What a firewall doesn't do

A firewall is an important layer, but it isn't a complete security strategy.

• It can't stop every phishing attack. DNS filtering and inspection can block some malicious links, but phishing works by convincing a person to act. Email security and training do most of the work there. See how to spot a phishing email.
• It doesn't remove malware already on a computer. That's the job of endpoint detection and response (EDR).
• It doesn't replace multi-factor authentication (MFA). Stolen passwords used to sign in look like normal, authorized traffic to a firewall.
• It doesn't protect data traveling between a remote user and a cloud app. Encryption handles that, and in some setups a VPN.

The zero trust model treats the firewall as one layer among many rather than the main defense. You need one, and you need the other layers too.

How NerdSquad manages firewalls for clients

We deploy, configure and manage business firewall hardware as part of our managed IT services. That includes initial setup based on your environment and compliance needs, rule changes as your business changes, firmware updates, and alerting on firewall events through our around-the-clock automated monitoring. A firewall that was installed and forgotten, running old firmware with default rules nobody has reviewed in years, provides a fraction of the protection of one that's actively managed. It's part of the layered approach described on our cybersecurity services page.

Quick recap

• A firewall is a traffic checkpoint for your network that controls what gets in and out based on rules.
• Hardware firewalls protect the whole network; software firewalls protect individual devices. Use both.
• Next-generation firewalls add deep packet inspection, application awareness, intrusion prevention, DNS filtering and logging.
• A firewall alone won't stop phishing, malware already on a device or stolen passwords. It's one layer of several.

Talk to NerdSquad

Already a client? Call (239) 465-0079 or submit a ticket. If something is down, call so we can start right away.

Not a client yet? NerdSquad Managed IT Services is a Managed Service Provider (MSP) based in Naples, Florida. We support businesses onsite across Southwest Florida and remotely nationwide. Book a discovery call or call (239) 465-0079.

Related: Cybersecurity services for businesses