Cyber Security
Internet and Its Uses
A monitors the traffic entering and leaving a network or device and blocks anything that does not meet its security rules.
A firewall sits between the trusted internal network and the outside internet. It examines each packet against a set of rules (criteria) and allows through only the traffic that is permitted, blocking the rest. It can keep a list of blocked or allowed addresses, and it helps prevent unauthorised access and stops malware from communicating out to an attacker. A firewall can be hardware, software, or both.
Common exam question
Drawing how a firewall works or data is intercepted
Question: Draw and annotate a diagram to show how a firewall works, or how data is intercepted as it travels (4 marks).
Asked in 2 of the 17 papers. Each point the diagram shows earns a mark, so make every point a label or an arrow (a DDoS drawing is marked the same way). For a firewall between a network and the internet, show any four of: traffic passing through it in both directions; criteria (rules) set on it; traffic compared with the criteria; traffic rejected, and traffic accepted, according to whether it meets them. One-way arrows miss the first point.
For data interception, show any four of: data travelling between two devices; the data examined while in transit; a packet sniffer doing it; the captured data passed to a third party who analyses it for anything useful; or the connection hacked to spoof the destination address.