The Evolution of Network Security: From Firewalls to VPN to ZTNA 

For decades, organisations have relied on layered defences to protect their digital assets. But as technology, work habits, and cyber threats evolved, so too did the tools we use. The journey from firewalls to VPNs to Zero Trust Network Access (ZTNA) reflects not only the technological landscape but also the fundamental rethinking of how we secure trust in an increasingly perimeter-less world. 

Firewalls: The First Line of Defence

In the early days of enterprise networking, security was largely about keeping the bad guys out. Firewalls emerged in the 1980s and 1990s as gatekeepers that filtered traffic between internal networks and the outside world. 

The approach was to block or allow traffic based on rules such as IP addresses, ports, and protocols. This was largely speaking a simple way to effectively protect organisations against external threats, and it formed the foundations for perimeter-based security. 

However, firewalls assume a clear boundary. For example, if a user is inside the network, then they must be trusted, if a user is outside the network they cannot be untrusted. Once attackers bypassed the firewall or gained insider access, defences were thin. 

The firewall era represents a “castle-and-moat” model: secure the perimeter, and everything inside is assumed safe. 

Virtual Private Networks (VPN): Expanding the Perimeter

As businesses became more distributed and remote working increased, the firewall-only approach struggled. Employees needed secure remote access, and partners required connectivity. VPNs became the answer in the late 1990s and 2000s. 

The approach was to encrypt traffic between remote users and corporate networks, creating a secure “tunnel.”  This enabled secure remote work, protected data in transit, whilst extending the trusted perimeter. 

However, VPNs grant broad network access once connected, often more than needed. It can also create complications for global workforces and scaling for large organisations.  

VPNs extended the “moat,” but the trust model remained flawed: once inside, users could often move laterally across the network. 

Zero Trust Network Access (ZTNA): Trust No One, Verify Everything

With the rise of cloud adoption, SaaS, mobile workforces, and sophisticated cyber threats, the traditional perimeter dissolved. Enter Zero Trust, first conceptualised by Forrester in 2010. ZTNA emerged as a practical implementation. 

ZTNA is based on a ‘Never trust, always verify’ model. This means that by default every user, device, and request is verified. Access is contextual, least-privileged, and often application-specific. 

This allows admins granular access control, meaning employees can have restricted access to specific applications, without having access to the entire network. 

The authentication process is adaptive, based on identity, device posture, and context. It is cloud-native scalability and offers an improved user experience over clunky VPNs. 

ZTNA represents a paradigm shift, security is no longer about protecting a perimeter but about securing access everywhere, for everyone, all the time. 

ZTNA is not the endpoint but part of a broader trend. Offerings like Secure Access Service Edge (SASE) integrates ZTNA, firewall-as-a-service, secure web gateways, and more into a cloud-delivered model.  

The trajectory is clear: security is moving closer to the user and the application, with identity and context at the centre. 

How Zscaler Delivers Zero Trust Network Access (ZTNA) for Secure, Modern Connectivity

Zscaler is a cloud-native security platform that delivers Zero Trust Network Access (ZTNA) as part of its broader Secure Access Service Edge (SASE) offering. Instead of relying on traditional VPNs that provide broad, network-level access, Zscaler applies the Zero Trust principle of “never trust, always verify.” Users and devices are authenticated and authorised on a per-session, per-application basis, ensuring least-privileged access. 

Zscaler sits between users and the applications they need whether hosted in the data centre, public cloud, or SaaS without ever placing users on the corporate network. This architecture eliminates lateral movement, reduces attack surfaces, and simplifies policy enforcement. Because it’s delivered from a global cloud, Zscaler also ensures low-latency, scalable access for distributed workforces. 

In essence, Zscaler modernises secure access by replacing VPNs with identity-driven, application-specific connectivity, helping organisations embrace digital transformation and hybrid work while reducing cyber risk. 

The journey from firewalls to VPNs to ZTNA illustrates how security must evolve to match the realities of a changing digital world. From perimeter defence to remote access, to zero trust, each phase has addressed the weaknesses of the previous. Organisations that embrace this evolution are better positioned to protect their data, users, and future in a borderless, cloud-driven world.