The primary function of firewall in network security is

Correct answer: To filter incoming and outgoing network traffic based on security rules

Explanation: A firewall's primary role is to enforce network security policies by inspecting network traffic and allowing or blocking connections according to configured rules (such as IP addresses, ports, protocols, and application-level criteria).

• Packet-filtering firewalls examine packet headers and make allow/deny decisions based on IPs and ports.

• Stateful inspection firewalls track connection state and can make context-aware decisions.

• Application-layer firewalls (proxies) inspect application traffic and can enforce more granular rules.

Why the other choices are incorrect:

• "To monitor network traffic and detect anomalies." — This describes intrusion detection/monitoring systems; while firewalls can log traffic and contribute to detection, active monitoring and anomaly detection are separate functions.

• "To create virtual private networks for secure communication." — VPNs establish encrypted tunnels using VPN protocols or gateways; a firewall may allow or block VPN traffic but does not create the VPN tunnel itself.

• "To encrypt data before Transmission." — Encryption is performed by cryptographic protocols such as TLS or IPSec. Firewalls do not provide end-to-end encryption, though they may handle or inspect encrypted traffic when configured to do so.