When a client computer initiates contact with a server to request a specific service, which of the following is used?

When a client computer initiates contact with a server to request a specific service, which of the following is used?

• A. Port numbers
• B. IP address
• C. Domain name
• D. MAC address

Answer: (A)

Port numbers identify which specific service on a host the client wants to use. When a client wants to reach a service, it sends a request to the server’s IP address and to the destination port that corresponds to that service (for example, port 80 for HTTP, 443 for HTTPS). The server listens on these ports and hands incoming connections to the correct application or service. The client also uses a temporary source port, but the key piece that tells the server which service to provide is the destination port. An IP address identifies the host device itself, not the particular service. A domain name is just a human-friendly label that resolves to an IP address. A MAC address is a hardware address used on the local network segment for frame delivery and isn’t used to reach a service on a remote host.

Port numbers identify which specific service on a host the client wants to use. When a client wants to reach a service, it sends a request to the server’s IP address and to the destination port that corresponds to that service (for example, port 80 for HTTP, 443 for HTTPS). The server listens on these ports and hands incoming connections to the correct application or service. The client also uses a temporary source port, but the key piece that tells the server which service to provide is the destination port.

An IP address identifies the host device itself, not the particular service. A domain name is just a human-friendly label that resolves to an IP address. A MAC address is a hardware address used on the local network segment for frame delivery and isn’t used to reach a service on a remote host.