- A
HTTP/HTTPS: TCP 80/443; FTP control: TCP 21; SSH: TCP 22; Telnet: TCP 23; DNS: UDP 53
This is correct because HTTP and HTTPS use TCP ports 80 and 443 respectively, FTP control uses TCP port 21, SSH uses TCP port 22, Telnet uses TCP port 23, and DNS primarily uses UDP port 53. These are standard port assignments as per IANA and Cisco documentation.
- B
HTTP/HTTPS: TCP 80/443; FTP control: TCP 20; SSH: TCP 22; Telnet: TCP 23; DNS: TCP 53
Why wrong: This is incorrect because FTP control uses TCP port 21, not 20. Port 20 is used for FTP data transfer. Also, DNS primarily uses UDP port 53, not TCP, although TCP can be used for zone transfers or large responses.
- C
HTTP/HTTPS: UDP 80/443; FTP control: TCP 21; SSH: TCP 22; Telnet: TCP 23; DNS: UDP 53
Why wrong: This is incorrect because HTTP and HTTPS use TCP, not UDP. TCP provides reliable, connection-oriented communication required for web traffic. UDP is connectionless and does not guarantee delivery.
- D
HTTP/HTTPS: TCP 80/443; FTP control: TCP 21; SSH: TCP 22; Telnet: TCP 23; DNS: TCP 53
Why wrong: This is incorrect because DNS primarily uses UDP port 53, not TCP. While DNS can use TCP for zone transfers or when responses exceed 512 bytes, the default and most common transport is UDP.
Quick Answer
The correct answer pairs HTTP/HTTPS with TCP 80/443, FTP control with TCP 21, SSH with TCP 22, Telnet with TCP 23, and DNS with UDP 53, as these represent the default transport protocols and ports for IP services in a basic CCNA context. This mapping is rooted in the fundamental distinction between TCP’s connection-oriented reliability—essential for web browsing, file transfers, and remote administration—and UDP’s connectionless efficiency, which suits DNS queries that prioritize speed over overhead. On the CCNA 200-301 v2 exam, you will often see these pairings in drag-and-drop or multiple-choice questions testing your ability to match services to their well-known ports, with a common trap being the assumption that DNS always uses TCP; remember that standard queries use UDP 53, while TCP 53 is reserved for zone transfers outside the basic context. A reliable memory tip is to recall that all services requiring session persistence—HTTP, HTTPS, FTP, SSH, and Telnet—use TCP, while lightweight protocols like DNS, DHCP, NTP, and Syslog default to UDP.
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: dNS commonly uses UDP port 53 for resolving domain names to IP addresses, which is essential for network communication and troubleshooting in Cisco environments.. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Match each IP service to the transport protocol and default port it commonly uses in a basic CCNA context.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
HTTP/HTTPS: TCP 80/443; FTP control: TCP 21; SSH: TCP 22; Telnet: TCP 23; DNS: UDP 53
DNS primarily uses UDP port 53 for standard queries due to low overhead; TCP 53 is used for zone transfers but not in basic CCNA context. DHCPv4 server uses UDP port 67 because the protocol relies on broadcasts and does not require a connection-oriented transport. NTP uses UDP port 123 to keep time synchronization lightweight and efficient. Syslog uses UDP port 514 to send system messages without requiring a session, prioritizing speed over reliability.
Key principle: DNS commonly uses UDP port 53 for resolving domain names to IP addresses, which is essential for network communication and troubleshooting in Cisco environments.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
HTTP/HTTPS: TCP 80/443; FTP control: TCP 21; SSH: TCP 22; Telnet: TCP 23; DNS: UDP 53
- ✗
HTTP/HTTPS: TCP 80/443; FTP control: TCP 20; SSH: TCP 22; Telnet: TCP 23; DNS: TCP 53
- ✗
HTTP/HTTPS: UDP 80/443; FTP control: TCP 21; SSH: TCP 22; Telnet: TCP 23; DNS: UDP 53
- ✗
HTTP/HTTPS: TCP 80/443; FTP control: TCP 21; SSH: TCP 22; Telnet: TCP 23; DNS: TCP 53
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓HTTP/HTTPS: TCP 80/443; FTP control: TCP 21; SSH: TCP 22; Telnet: TCP 23; DNS: UDP 53Correct answer▾
Why this is correct
This is correct because HTTP and HTTPS use TCP ports 80 and 443 respectively, FTP control uses TCP port 21, SSH uses TCP port 22, Telnet uses TCP port 23, and DNS primarily uses UDP port 53. These are standard port assignments as per IANA and Cisco documentation.
✗HTTP/HTTPS: TCP 80/443; FTP control: TCP 20; SSH: TCP 22; Telnet: TCP 23; DNS: TCP 53Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that FTP control port is 21, not 20, and DNS primarily uses UDP, not TCP.
Why candidates choose this
Candidates often confuse FTP control (21) with FTP data (20) and may think DNS uses TCP because of zone transfers.
✗HTTP/HTTPS: UDP 80/443; FTP control: TCP 21; SSH: TCP 22; Telnet: TCP 23; DNS: UDP 53Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that HTTP/HTTPS use TCP, not UDP.
Why candidates choose this
Candidates might think HTTP/HTTPS can use UDP due to the existence of HTTP/3 (QUIC), but in basic CCNA context, they use TCP.
✗HTTP/HTTPS: TCP 80/443; FTP control: TCP 21; SSH: TCP 22; Telnet: TCP 23; DNS: TCP 53Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that DNS primarily uses UDP, not TCP.
Why candidates choose this
Candidates may know DNS can use TCP and incorrectly assume it is the primary protocol, or they may confuse it with other services that use TCP.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Be careful not to confuse FTP control (21) with FTP data (20). Also, remember that DNS primarily uses UDP, not TCP, even though it can use TCP in certain scenarios. HTTP/HTTPS always use TCP in a basic CCNA context; do not be misled by newer protocols like QUIC.
Detailed technical explanation
How to think about this question
IP services such as DNS, DHCP, NTP, and Syslog are fundamental to network operations and management in Cisco environments. DNS (Domain Name System) translates human-readable domain names into IP addresses, using UDP port 53 for standard queries. DHCP (Dynamic Host Configuration Protocol) automates IP address assignment using UDP port 67 on the server side, simplifying network administration. NTP (Network Time Protocol) synchronizes device clocks using UDP port 123, which is crucial for accurate logging and security functions. Syslog transmits event messages to centralized servers over UDP port 514, enabling effective monitoring and troubleshooting of Cisco devices. These IP services use UDP as their transport protocol primarily because UDP offers low latency and minimal overhead, which suits the query-response and event-driven nature of these protocols. Cisco devices and network engineers rely on these default port assignments to configure access control lists (ACLs), firewall rules, and monitoring tools correctly. Recognizing these defaults is essential for troubleshooting connectivity issues and ensuring that critical services are not inadvertently blocked by security policies. A common exam trap involves confusing the transport protocol or port number for these services, such as assuming DNS uses TCP by default or mixing DHCP server and client ports. In practical Cisco network scenarios, these defaults are rarely changed, so knowing them precisely helps avoid misconfigurations. For example, blocking UDP port 67 would prevent DHCP address assignment, causing network outages. Understanding the practical behavior of these services and their default ports is vital for both exam success and real-world Cisco network management.
KKey Concepts to Remember
- DNS commonly uses UDP port 53 for resolving domain names to IP addresses, which is essential for network communication and troubleshooting in Cisco environments.
- DHCPv4 server traffic uses UDP port 67 to allocate IP addresses dynamically to hosts, enabling automated IP configuration in Cisco networks.
- NTP uses UDP port 123 to synchronize clocks across network devices, ensuring accurate time stamps for logs and security protocols in Cisco systems.
- Syslog uses UDP port 514 to send event messages from network devices to centralized logging servers, aiding in network monitoring and troubleshooting.
- Transport protocols like UDP are preferred for these services due to their low overhead and suitability for query-response or event-driven communication in Cisco networks.
- Understanding default port assignments helps network engineers configure ACLs and firewall rules accurately to permit or restrict specific IP services.
- Cisco devices rely on these default ports for IP services unless explicitly reconfigured, making knowledge of these defaults critical for CCNA exam scenarios.
- Misidentifying the transport protocol or port number can lead to misconfigured security policies or troubleshooting errors in Cisco network environments.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
DNS commonly uses UDP port 53 for resolving domain names to IP addresses, which is essential for network communication and troubleshooting in Cisco environments.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
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FAQ
Questions learners often ask
What does this 200-301 question test?
Network Services and Security — This question tests Network Services and Security — DNS commonly uses UDP port 53 for resolving domain names to IP addresses, which is essential for network communication and troubleshooting in Cisco environments..
What is the correct answer to this question?
The correct answer is: HTTP/HTTPS: TCP 80/443; FTP control: TCP 21; SSH: TCP 22; Telnet: TCP 23; DNS: UDP 53 — DNS primarily uses UDP port 53 for standard queries due to low overhead; TCP 53 is used for zone transfers but not in basic CCNA context. DHCPv4 server uses UDP port 67 because the protocol relies on broadcasts and does not require a connection-oriented transport. NTP uses UDP port 123 to keep time synchronization lightweight and efficient. Syslog uses UDP port 514 to send system messages without requiring a session, prioritizing speed over reliability.
What should I do if I get this 200-301 question wrong?
Review dNS commonly uses UDP port 53 for resolving domain names to IP addresses, which is essential for network communication and troubleshooting in Cisco environments., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
DNS commonly uses UDP port 53 for resolving domain names to IP addresses, which is essential for network communication and troubleshooting in Cisco environments.
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Last reviewed: May 17, 2026
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