Firewall
A firewall is a device or piece of software that sits between your computers and the internet and decides, using a set of rules, which traffic is allowed through. Firewalls are the first of the five Cyber Essentials controls. Every in-scope device must be protected by one, which the 2026 question set checks at A4.1 and A4.1.1.
- Term
- Firewall
- Also known as
- Network firewall, Hardware firewall
- Category
- Networks and firewalls
- Requirement area
- 1. Firewalls
- Reviewed against
- Requirements v3.3
What does the term firewall mean in Cyber Essentials?
A firewall is a device or piece of software that sits between your computers and the internet and decides, using a set of rules, which traffic is allowed through.
All devices run network services to allow them to communicate with other devices and services. By restricting access to these services, you reduce your exposure to attacks. You can do this using firewalls or network devices with firewall functionality.
How does firewall apply to Cyber Essentials?
In plain terms
Think of a firewall as the receptionist at your office front door. Visitors from outside can only get past if they are on the list, and anyone unexpected is turned away. A firewall does the same for internet traffic: it checks where each connection comes from and where it is going, then allows or blocks it.
There are two kinds you will meet. A boundary firewall protects a whole office network, and is often built into your broadband router. A software firewall runs on a single laptop or server and protects that device wherever it goes.
What Cyber Essentials asks
The requirements say: "You must protect every device in scope with a correctly configured firewall (or network device with firewall functionality)." For every firewall you must change the default admin password, keep the admin interface off the internet unless there is a documented need and MFA or an IP allow list, block unauthenticated inbound connections by default, have inbound rules approved and documented, and remove rules you no longer need.
In the 2026 question set this is A4.1 to A4.11. A4.1.1 asks whether software firewalls are enabled on all computers, laptops and servers, even those sitting behind an office firewall.
What an assessor looks for
- The make and model of each router and firewall, listed at A2.5.
- A software firewall switched on for laptops that leave the office, because the requirements say to use one "on devices which are used on untrusted networks, such as public wifi hotspots".
- Firmware that is still supported by the vendor, because A6.1 treats firewall and router firmware as an operating system.
Read the full firewall requirements or start with A4.1.
Related terms
- Boundary firewallA boundary firewall is a network device that restricts inbound and outbound traffic between an organisation's network and the internet using firewall rules.
- RouterA router is the box that connects your office or home network to the internet and passes traffic between the two.
- Software firewallA software firewall is a firewall configured on a device that works like a boundary firewall but only protects the single device on which it is configured.
- Firewall ruleA firewall rule is a single instruction on a firewall that says which traffic to allow or block, based on where it comes from, where it is going and what type it is.
- Guest Wi-FiGuest Wi-Fi is a separate wireless network for visitors that lets them reach the internet without joining the network your staff and business systems use.
- Inbound connectionAn inbound connection is a connection that someone on the internet starts towards a device or service inside your network, rather than one your own devices start.
Frequently asked questions
A firewall is a device or piece of software that sits between your computers and the internet and decides, using a set of rules, which traffic is allowed through. The definition follows the NCSC's Cyber Essentials: Requirements for IT Infrastructure v3.3.
In the 2026 Danzell question set, firewall comes up at A4.1, A4.1.1, A4.2, A4.7. Read those questions against the definition above so your answers use the term the way the assessor will.
Firewall relates to 1. Firewalls in the NCSC's Cyber Essentials: Requirements for IT Infrastructure v3.3. Read that section for the control your answers must show.
Would you pass the 2026 question set?
Answer 24 yes or no questions, built by the assessors who mark Cyber Essentials, and get a readiness score in about five minutes, with any auto-fail questions you miss flagged first in your results.