A client packet is received by a server. The packet has a destination port number of 53. What service is the client requesting?
- DNS
- NetBIOS (NetBT)
- POP3
- IMAP
Explanation: The transport layer utilizes destination port numbers to identify the specific application or service being requested on a destination server. According to the standard assignments defined by the Internet Assigned Numbers Authority (IANA), port 53 is categorized as a well-known port reserved specifically for the Domain Name System (DNS). When a server receives a packet with this destination port, it recognizes that the client is requesting a name resolution service, typically to translate a human-readable domain name into its corresponding numeric IP address. While other services such as POP3 or IMAP utilize their own designated well-known ports (110 and 143 respectively) to facilitate email retrieval, port 53 remains the global standard for DNS queries and responses using both UDP and TCP transport protocols.
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