What does a firewall primarily protect a network from?

A firewall primarily protects a network from unauthorized access. Firewalls serve as a barrier between a trusted internal network and untrusted external networks, such as the internet. They monitor and control incoming and outgoing network traffic based on predetermined security rules, effectively blocking malicious activities and unauthorized attempts to access sensitive information or resources. This capability is crucial for maintaining the integrity and confidentiality of data within the network, ensuring that only legitimate users can connect and interact with network resources.

The other options represent different concerns that firewalls do not specifically address. Physical damage relates to the infrastructure of the network rather than the data transfer processes, network congestion involves bandwidth and traffic management rather than security per se, and power outages pertain to electricity supply and system uptime rather than cybersecurity threats. Thus, the main focus of a firewall is on preventing unauthorized access to safeguard the network's security.