Final answer:
A network switch uses a MAC address to determine which port to use when sending frames to a host with a specific IPv4 address, by referring to its MAC address table, and may use ARP if necessary.
Step-by-step explanation:
The question pertains to networking, specifically the operation of a network switch and IPv4 addressing. When a switch needs to send frames to a specific host, it uses the MAC address associated with the IPv4 address of the host. This process involves the switch consulting its MAC address table, also known as a CAM table (Content Addressable Memory), which maps MAC addresses to specific ports on the switch. To determine the correct MAC address, the switch might have previously learned this information by examining frames that have passed through it, or it may use ARP (Address Resolution Protocol) to resolve the IPv4 address to a MAC address.
Once the switch has the MAC address, it will use the port associated with that address to send the frame to the host. If the address is unknown or the ARP process is needed, the switch might initially send an ARP broadcast to the entire network. After the host replies with its MAC address, the switch updates the MAC address table and can then forward frames to the correct port efficiently. It's important to note that switches operate at the data link layer (Layer 2) of the OSI model and therefore primarily use MAC addresses for forwarding decisions rather than IP addresses.