ISC2 Certified in Cybersecurity (CC) Practice Question
On a single server hosting both a website and an SMTP email service over the same IP address, what allows the operating system to direct incoming traffic to the correct application process?
The subnet mask configured on the server
The Time-to-Live (TTL) field in the IP header
The MAC address of the network interface card
The destination port number in the TCP or UDP header
Ports are 16-bit numerical identifiers used in the headers of TCP and UDP segments. When packets arrive at a host, the destination port number tells the operating system which listening socket-and therefore which application process-should handle the data (for example, port 80 or 443 for web traffic, port 25 for SMTP). A MAC address only identifies the network interface at the data-link layer, a subnet mask helps determine network boundaries for routing, and the Time-to-Live (TTL) field simply limits a packet's lifespan on the network. None of those fields perform per-application delivery on the host; only the destination port does.
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ISC2 Certified in Cybersecurity (CC)
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