A client packet is received by a server. The packet has a destination port number of 110. What service is the client requesting?
- DNS
- DHCP
- SMTP
- POP3
Explanation: The transport layer utilizes destination port numbers to identify the specific service or application being requested on a server. According to the standard port assignments defined by the Internet Assigned Numbers Authority (IANA), port 110 is reserved as a well-known port for the Post Office Protocol version 3 (POP3). When a server receives a packet with this destination port, it recognizes that the client is requesting to establish a connection for retrieving email messages. While other ports are used for different mail services—such as port 25 for SMTP or port 143 for IMAP—port 110 specifically signals the server to direct the traffic to the POP3 application process to facilitate the download of mail to the client's local application.
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