Which of the following is commonly used to block or allow network ports such…

Correct answer: Firewall.

A firewall is a network security system that monitors and controls incoming and outgoing traffic based on a set of predefined rules. It works at the network boundary and can permit or deny traffic by inspecting the port number and protocol of each packet — for example, allowing HTTP traffic on port 80 and blocking SSH traffic on port 22 (or vice versa). This makes it the standard tool for blocking or allowing specific network ports.

Why the other options are wrong:

• Compiler — a program that translates source code into machine code; it has nothing to do with network traffic.

• Load Balancer — distributes incoming traffic across multiple servers for availability and performance; it does not act as a security gate that opens or closes ports.

• Web Browser — a client application used to access websites; it consumes services but does not control port access.

• Database Server — stores and serves data to applications; it is a service running behind ports, not the mechanism that controls them.