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

The primary purpose of a firewall in network security is to filter incoming and outgoing network traffic. Firewalls serve as a barrier between a trusted internal network and untrusted external networks, such as the internet. By examining data packets entering or leaving the network based on predetermined security rules, firewalls help prevent unauthorized access and protect against various threats, such as malware and attacks.

Firewalls can be configured to allow or block specific traffic based on factors such as source and destination IP addresses, port numbers, and protocols. This ability to control traffic flow is critical in establishing and maintaining a secure network environment. They play a crucial role in enforcing the organization's security policies and assisting in compliance with regulatory requirements.

The other options pertain to different areas of IT security. Encrypting sensitive data, for instance, involves securing data at rest or in transit to ensure confidentiality, distinct from the filtering functions of a firewall. Storing backup copies of data relates to data recovery and business continuity, while user authentication deals with verifying identities before granting access to systems or services. Each of these functions is important in an overall security strategy, but they do not define the core role of a firewall.