Which of the following protocols uses both TCP and UDP ports?

D

The protocol that uses both TCP and UDP ports is DNS (Domain Name System).

TCP is a connection-oriented protocol that ensures the reliability of the data transmission by establishing a virtual connection between the two endpoints before the data exchange. UDP, on the other hand, is a connectionless protocol that does not guarantee the delivery or reliability of data.

DNS is a protocol used to resolve domain names to IP addresses. It uses TCP port 53 for zone transfer and larger queries that require reliability, and UDP port 53 for smaller queries that do not require reliability.

The DNS server listens on both TCP and UDP ports 53 to receive DNS queries from the clients. If the query is small enough, it will be sent over UDP, and if it is too large or requires reliability, it will be sent over TCP.

SMTP (Simple Mail Transfer Protocol) uses TCP port 25 to send email messages between email servers. Telnet uses TCP port 23 to establish a remote terminal connection to a network device. FTP (File Transfer Protocol) uses TCP port 21 to establish a connection and transfer files between a client and server. None of these protocols use UDP.