What firewalls can—and can’t—accomplish

Firewalls were born in the 1990s, alongside Windows 95 and Internet Explorer. They’ve been a staple of network security since, which prompts the question: Are firewalls still relevant? The determining factor is whether firewalls have grown with the changes we’ve seen in technology or if they’ve just stayed in line with the technology of the 1990s and early 2000s.

How Firewalls Work & How They Don’t

Firewalls work primarily on the principle of deep packet inspection. Data packets are the units of information that constitute any type of Internet traffic, including Web traffic. They protect networks by checking the payload of every data packet trying to enter or leave a network and blocking any packets that contain malicious content. Content typically is defined as malicious through a series of rather complex policies and rules.

Today, data is almost always encrypted. Encryption ensures that good incoming and outgoing traffic is protected from prying eyes, but, unfortunately, it also hides bad incoming and outgoing traffic. Some firewalls can de-encrypt data packets, check their payload, and then re-encrypt them, but this process is computationally intensive and can bog down the network significantly. Also, this process is not always an available option given how many modern security protocols block the types of man-in-the-middle operations required for full-blown SSL inspection.

Leveraging IP Addresses

Indeed, deep packet inspection is becoming an antiquated security practice, but there are other ways to identify whether specific activity is malicious.

For example, some organizations blacklist malicious Web domains, then automatically block traffic from those sites, while others use tactics such as SIEM log analysis. However, these types of monitoring and alert systems are reactive: They tell you that you’ve been attacked, but don’t block the malicious traffic that can cause an attack.

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