ITPEC FE Morning April 2019 Question 35

TELNET — a remote terminal session needs a reliable, ordered byte stream, so TELNET runs over TCP (port 23).

A TELNET user types commands and reads the output over a long-lived session; a lost or reordered keystroke would corrupt it, so it relies on the connection, acknowledgements and retransmission of TCP. The other three are short request and response exchanges that run over UDP.

Answer (c)

Why not others:

• •(a) DHCP — UDP ports 67 and 68; a client asking for an address has no IP address yet and must broadcast, which TCP cannot do
• •(b) SNMP — UDP ports 161 and 162; small, frequent polling messages where setting up a connection would be overhead
• •(d) TFTP — UDP port 69; the trivial version of FTP with its own simple acknowledgements, unlike FTP itself, which uses TCP

Key rule: Session-oriented protocols such as TELNET, SSH, FTP, SMTP and HTTP use TCP; lightweight or broadcast ones such as DHCP, SNMP, TFTP and most DNS queries use UDP.

Networks · AI-written, may contain errors