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What is zero trust?
Zero trust is a security model built on one idea: never trust, always verify. Instead of assuming everything inside a corporate network is safe, zero trust checks every user, device and application, every time they try to connect, regardless of where they're connecting from.
Traditional network security worked like a castle with a moat. Once you were inside the perimeter, you were trusted. That model doesn't hold up anymore. Your people work from anywhere, your applications live across multiple clouds, and your data moves between them constantly. Zero trust replaces the moat with continuous verification at every point in the network.
The core principle: never trust, always verify
Zero trust starts from the assumption that a breach has already happened, or will. Every request for access gets treated as if it came from an open network, even if it's a user who logged in five minutes ago from a company laptop.
That means:
- Verify explicitly. Check identity, location, device health and behaviour every time, not just at login
- Use least-privilege access. Give users and systems only the access they need for the task in hand, and nothing more
- Assume breach. Design the network so that if one part is compromised, the damage stays contained
This isn't about adding friction for its own sake. Done well, zero trust verifies constantly in the background, so your people barely notice it while attackers find far fewer places to hide.
Zero trust architecture: the components
Zero trust architecture (ZTA) is the practical implementation of these principles across your network. The US National Institute of Standards and Technology's SP 800-207 is the standard reference framework, and most enterprise zero trust deployments build on its core components:
- Identity verification. Multi-factor authentication and continuous identity checks confirm who's asking for access, not just once, but throughout the session
- Micro-segmentation. The network gets divided into small, isolated zones, so a compromised device or credential can't move freely to reach other systems
- Least-privilege access control. Access policies are granted per session, based on identity, device posture and context, rather than broad, standing permissions
- Continuous monitoring. Traffic and behaviour get analysed in real time, so unusual activity gets flagged and contained fast
Together, these components shrink the attack surface and make lateral movement across the network much harder for anyone who does get in.
Why zero trust matters now
Digital transformation has changed what enterprise networks need to protect. As organisations migrate workloads to multi-cloud environments and support hybrid working at scale, the traditional network perimeter has effectively disappeared. Data and applications sit across public cloud, private cloud and on-premises infrastructure, all connected to a growing number of devices and locations.
That complexity is exactly why zero trust has moved from a niche security approach to a mainstream requirement for CIOs, CTOs and heads of network infrastructure. It gives you a consistent security model that works the same way whether your people and workloads sit in a data centre, a public cloud or a home office.
Zero trust and SASE and SD WAN
Zero trust doesn't operate in isolation. It's most effective when it's built into the network itself, not bolted on afterwards. That's where secure access service edge (SASE) and SD WAN come in.
SASE combines networking and security into a single, cloud-delivered service, applying zero trust principles like identity verification and least-privilege access at every point where users connect. SD WAN gives you the intelligent, software-defined network foundation that routes traffic securely and efficiently across sites and clouds.
Colt's network connects 900+ data centres across a 32,000+ km fibre network, giving your SASE and SD WAN deployment the low-latency, on-net reach it needs to enforce zero trust consistently, wherever your business operates.
Frequently asked questions
What is zero trust in simple terms?
Zero trust is a security approach that checks every user and device before granting access, every time, rather than trusting anything just because it's already inside the network.
What is zero trust architecture?
Zero trust architecture is the practical framework for applying zero trust principles across a network. It typically includes identity verification, micro-segmentation, least-privilege access control and continuous monitoring, based on standards like NIST SP 800-207.
How is zero trust different from a VPN?
A VPN grants broad access to a network once a user connects. Zero trust verifies identity and context continuously, and only grants access to the specific application or resource a user needs, not the whole network.
How does zero trust relate to SASE?
SASE applies zero trust principles as part of a combined networking and security service, delivered from the cloud. It enforces identity checks and least-privilege access at every connection point across your network.
Do small and medium businesses need zero trust?
Yes. Zero trust scales to any size of organisation. As soon as your people work across multiple locations, devices or clouds, the traditional perimeter no longer protects you, whatever your size.
