220-1101 - Networking (20% of the exam) - Section 2.1

Compare and contrast TCP and UDP ports, protocols, and their purposes, including common well-known port numbers and their associated services.

Identify common well-known TCP and UDP ports and the service running on each - HTTP (80), HTTPS (443), SSH (22), RDP (3389), DNS (53), SMTP (25), and DHCP (67/68) among them - and distinguish connection-oriented TCP from connectionless UDP. Recognise which protocols are insecure (Telnet, FTP, HTTP) and the secure replacement a technician should prefer.

TCP and UDPWell-known portsHTTPS port 443RDP port 3389

Practice question for this objective

Free sampleNetworkingmedium

Priya administers a Linux server in a branch office and needs to manage it remotely over an encrypted command-line session. The perimeter firewall blocks all inbound traffic by default. Which single TCP port should she open to allow this secure remote administration?

APort 23, so the Telnet service can accept the remote management session from her workstation
BPort 22, so the SSH service can accept the encrypted remote management session she needs Correct
CPort 3389, so the RDP service can accept the encrypted remote management session she needs
DPort 21, so the FTP service can accept the remote management session from her workstation

Secure remote command-line administration uses SSH on TCP port 22, replacing the clear-text Telnet service on port 23. SSH encrypts authentication and the interactive shell over a single TCP connection on port 22, giving confidentiality that Telnet on 23 cannot, which is why 22 is the port to open for encrypted remote management.

Why A is wrong: Telnet does use port 23, but it sends credentials and commands in clear text, so it is the insecure choice rather than the encrypted session required.

Why B is correct: SSH listens on TCP 22 and encrypts the entire command-line session, which is exactly the secure remote administration Priya requires.

Why C is wrong: RDP on 3389 is encrypted, but it delivers a graphical Windows desktop, not the command-line session for a Linux server described here.

Why D is wrong: FTP on 21 transfers files rather than providing an interactive shell, and its control channel is unencrypted, so it fits neither requirement.

See more 220-1101 practice questions, answers explained.

Exam traps in Networking

Answers that look right on this material and are not. Each one is a distractor from a different question in the 220-1101 bank for this domain.

TCP port 80, the default for unencrypted HTTP traffic between the browser and web server.
Why it is wrong: Port 80 is genuinely used for web traffic, but it carries plaintext HTTP with no TLS encryption, so it does not meet the encrypted requirement.
Telnet on TCP port 23, which offers a familiar interactive command-line session to the device.
Why it is wrong: Telnet on port 23 does give a command-line session, but it transmits credentials and data in plaintext, so it is the insecure protocol being replaced.
UDP opens a session with a three-way handshake and retransmits any lost segments, while TCP sends datagrams with no acknowledgement.
Why it is wrong: This is tempting because both protocols are real transport protocols, but the attributes are reversed: the handshake and retransmission belong to TCP, not UDP.

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