When ISMC's founder installed the first firewalls for a national government, security had a clean shape: one strong wall at the edge of the network, and a trusted interior behind it. That model held for a while. Then it didn't. The two decades since have rewritten the fundamentals of network defense — and understanding how we got here is the best guide to what to do next.
The perimeter era: one wall at the edge
The earliest firewalls, arriving in the late 1980s, were packet filters: they examined each packet's source, destination, and port against a list of rules, with no memory of the conversation a packet belonged to. By the mid-1990s, stateful inspection — popularized by Check Point — let firewalls track active connections and judge traffic in context. Soon after came application-proxy firewalls, which intercepted each protocol and inspected the contents of the traffic itself. This was the world of the Raptor Firewall, where ISMC's founder wrote the curriculum and deployed the technology across government and enterprise networks.
What every one of these shared was a single assumption: there is an inside and an outside, and the firewall is the gate between them. Secure the perimeter, and you secured the network.
The perimeter dissolves: a firewall on every stack
The trusted interior turned out to be a fiction. Once an attacker slipped past the edge — through a phished credential, a laptop carried in and out, a compromised vendor — the flat internal network let them move sideways with little resistance. As applications moved to the cloud and the workforce went remote, the very idea of an "inside" lost its meaning. There was no longer one edge to defend.
The response was to stop trusting the network and start enforcing security everywhere at once. Host-based firewalls built into every operating system meant each machine could defend itself. The distributed-firewall idea — articulated as early as 1999 — pushed policy out to every endpoint rather than concentrating it at a chokepoint. That logic matured into microsegmentation, where policy follows the workload itself, and into Zero Trust: a model, named in 2010 and codified by NIST in 2020, that treats every request as untrusted until proven otherwise, regardless of where it originates.
The arc is striking: we went from one firewall guarding the gate to, in effect, a firewall on every IP stack that joins the network. Defense moved from the edge to the workload.
From cleartext to encryption everywhere
The second transformation was just as profound and far faster. For the internet's first decades, most traffic crossed the wire in cleartext — email, web pages, logins, all readable by anyone positioned along the path. Encryption existed but was reserved for the sensitive few: a banking page, a checkout form.
That changed with remarkable speed. SSL appeared in the mid-1990s and evolved through TLS to today's TLS 1.3 (2018). The 2013 disclosures about mass network surveillance pushed the industry decisively toward encrypting everything. In 2015, Let's Encrypt began issuing free certificates and removed the last excuse not to; by 2018 browsers began openly marking plain HTTP sites as "Not Secure." The result is a near-complete reversal in roughly a decade.
Encryption is no longer just for the perimeter-facing edge, either. Internal, server-to-server ("east-west") traffic is increasingly encrypted too, and even DNS lookups now travel over encrypted channels. The assumption has flipped entirely: traffic is encrypted by default, and cleartext is the exception that demands justification.
Other shifts worth watching
The same forces that reshaped the firewall and the wire are still in motion. A handful of related trends define the current landscape:
Identity became the new perimeter
With no network edge to anchor to, who and what is connecting — verified by strong authentication and multi-factor — now carries the weight that a firewall once did.
The cloud erased the data center wall
Workloads spread across providers and regions. Security had to become portable, following the application instead of living in a building.
Security moved into code
With Infrastructure as Code, the network and its security rules are written as configuration rather than wired up by hand — so the whole topology can be reviewed before it's built, reproduced identically, and rebuilt in minutes. Like working from a recipe instead of cooking from memory, it makes security consistent, auditable, and easy to scale.
Encrypted traffic hides threats too
The same encryption that protects users also conceals attacks, driving demand for inspection and analytics that work without breaking privacy.
AI now sits on both sides
Attackers use it to scale and personalize; defenders use it to spot anomalies in volumes of traffic no human could review.
Visibility is the new bottleneck
With controls everywhere and traffic encrypted, the hard problem is no longer building walls — it's knowing what's actually happening across them.
Why this history matters to you
These weren't fashions; they were responses to how attackers actually behave. An organization still defending only its edge, or still moving any traffic in cleartext, is protecting against a threat model most of the industry moved on from years ago. A partner who has worked through each of these transitions can help you judge which shifts your environment genuinely needs, in what order, and which are simply noise. That's what ISMC is here to do.
Where does your network stand?
If your defenses still assume a trusted interior, or any of your traffic still travels in the clear, an assessment is the fastest way to find out — and to fix it.
Request an assessmentHistorical and statistical references: Palo Alto Networks and Check Point firewall histories; FireMon, "A Practical History of the Firewall"; NIST SP 800-207 (Zero Trust Architecture, 2020); Google HTTPS Transparency Report (2025); Let's Encrypt project statistics (2015–2025).