What is the primary purpose of using a firewall in a network?

The primary purpose of using a firewall in a network is to filter incoming and outgoing traffic. Firewalls serve as a security barrier between a trusted internal network and untrusted external networks, such as the internet. They analyze traffic based on predetermined security rules, allowing or blocking data packets according to these rules. This capability is essential in protecting networks from unauthorized access, data breaches, and various types of cyber threats, while also ensuring that legitimate traffic is allowed through to users and services.

In contrast to the correct answer, managing bandwidth is typically the domain of Quality of Service (QoS) policies rather than firewalls. While firewalls can influence traffic flow, their primary function does not include proactive bandwidth management. Increasing network speed is generally not a function of firewalls, as they can potentially introduce latency when filtering traffic. Creating VLANs (Virtual Local Area Networks) is also not a function of firewalls; VLANs are used to segment networks logically for improved performance and security, which is a different function entirely. Therefore, filtering traffic stands out as the clear and primary role of firewalls in network security.