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

A firewall is a network security device or software that monitors and filters incoming and outgoing network traffic based on predefined security rules. Its main function is to block unauthorized access to or from a private network, serving as a barrier between trusted internal networks and untrusted external networks (like the internet). Firewalls can be configured to allow specific types of traffic while blocking others based on the network administrator's rules. Option A is incorrect because firewalls do not typically perform encryption functions; this is handled by other security protocols like TLS/SSL. Option C is incorrect because the management of IP addresses is handled by DHCP or network administrators, not firewalls. Option D is incorrect because detecting and removing malware is primarily the function of antivirus software, not firewalls. Option E is incorrect because data compression is not the main function of a firewall; it focuses on security, not performance enhancement.