What common security control can be placed at the network boundary to prevent unauthorized access?

A firewall is a common security control that is strategically positioned at the network boundary to regulate and monitor incoming and outgoing network traffic based on predetermined security rules. Its primary purpose is to act as a barrier between a trusted internal network and untrusted external networks, such as the internet.

By allowing or blocking specific traffic, a firewall can prevent unauthorized access attempts from external sources. It can enforce policies that restrict access to certain services or ports, thereby safeguarding sensitive data and network resources. Firewalls can operate at various layers of the OSI model, with some focusing on packet filtering, while others may be application-layer firewalls that can analyze traffic more deeply.

In contrast, while an intrusion detection system is designed to monitor network traffic for suspicious activity and alert administrators, it does not block potentially malicious traffic. Encryption protects the confidentiality of data but does not prevent unauthorized access at the network boundary. Access control lists can be used within firewalls to define who can access specific resources but by themselves do not provide the necessary perimeter defense functions that a firewall offers.