What device can help prevent unauthorized network access?

An intrusion detection system (IDS) is designed to monitor network traffic for suspicious activity and potential threats. It analyzes patterns of traffic and can alert administrators to possible breaches or unauthorized access attempts. However, it primarily serves to detect incidents rather than actively prevent them.

On the other hand, a firewall functions as a barrier between a trusted internal network and untrusted external networks. It enforces security policies by controlling incoming and outgoing network traffic based on predetermined security rules. Firewalls can block unauthorized access attempts and prevent potentially harmful traffic from entering a network, making them essential for maintaining network security.

While routers and modems are critical components of networking, their main roles are to direct data packets and facilitate connectivity, respectively. They do not inherently provide security against unauthorized access without being configured with security features such as those found in firewalls. Therefore, when it comes to preventing unauthorized network access, the function of a firewall is what is needed.