Match each network protocol to its well-known port number.

Match each network protocol to its well-known…

Drag a concept onto its matching description — or click a concept then click the description.

Concepts

Matches

443

3389

Correct answer & explanation

✓

HTTP: 80

These are standard well-known port assignments as defined by IANA. Common confusions include swapping HTTP/HTTPS ports or mixing SSH with Telnet.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

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HTTP: 80
Why this is correct
HTTP's IANA-assigned well-known port is 80, where web servers listen for cleartext requests from clients. Any web URL such as http://example.com implicitly communicates with port 80 by default, carrying unencrypted HTTP methods like GET and POST. Because the traffic is plaintext, anything sent over port 80 — including HTTP headers and submit form values — can be intercepted and read by a network sniffer.
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HTTPS: 443
Why this is correct
HTTPS is not a separate application-layer protocol but HTTP running inside a TLS/SSL tunnel, and it defaults to TCP port 443. On this port the client and server perform the TLS handshake to exchange keys and verify the server's certificate before any HTTP data travels. All communication, including the request URI, headers, and response body, is encrypted end-to-end so eavesdroppers on port 443 capture only ciphertext.
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FTP: 21
Why this is correct
FTP uses two parallel TCP connections: a control connection on port 21 to carry protocol commands such as USER, PASS, and CWD, and a separate data connection for transferring files. The data connection uses port 20 in classic active mode, but in passive mode it uses any high port negotiated by the server. Port 21 itself is strictly for command and response messages, never for file payload.
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SSH: 23
Why it's wrong here
Port 23 is the well-known port for Telnet, an antiquated and insecure remote terminal protocol that sends usernames, passwords, and keystrokes in plaintext. SSH (Secure Shell) was designed as a secured replacement and uses port 22 instead. An SSH client that is configured to connect to port 23 will actually reach a Telnet server, producing a protocol mismatch or exposing credentials to interceptors.
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DNS: 80
Why it's wrong here
DNS has no relationship with port 80; it uses UDP port 53 for standard queries and TCP port 53 for zone transfers or any response that exceeds a single datagram. Port 80 is the reserved territory of HTTP web servers. If a DNS service were available on port 80, that would break the entrenched convention that intermediaries and firewalls rely on to classify traffic, and normal HTTP clients would receive meaningless DNS messages.
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SMTP: 53
Why it's wrong here
SMTP traffic never runs on port 53, because that port is the exclusive registered port for DNS. SMTP traditionally listens on TCP port 25 for mail exchange between servers, while email clients submit messages via port 587 or legacy 465 for implicit TLS. An MTA or client configured to use port 53 would try to send message data to a DNS resolver, which would not understand the MAIL/RCPT exchange and the mail delivery would fail.

CS0-003 Practice Question: Match each network protocol to its well-known…

Why each option matters

Option-by-option breakdown

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