CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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.
A host can reach remote websites by IP address but fails when using their hostnames. Which missing configuration item is the strongest suspect?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A DNS server address
When a host can reach remote websites by IP address but not by hostname, the issue is that the host cannot resolve the hostname to an IP address. DNS (Domain Name System) is responsible for this resolution, and if the DNS server address is missing or misconfigured on the host, name resolution fails. This is the strongest suspect because all other network connectivity (routing, switching) is functional, as proven by successful IP-based access.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
A DNS server address
Why this is correct
This is correct because the host needs DNS information to resolve hostnames.
Related concept
Read the scenario before looking for a memorised answer.
✗
A new MAC address
Why it's wrong here
This is wrong because hostname resolution does not depend on changing the host MAC address.
When this WOULD be correct
In a question about a network security scenario where a device's MAC address has changed due to a network policy update, and the question asks about connectivity issues related to access control lists (ACLs) or MAC filtering, a new MAC address could be the correct answer if it is preventing access to certain resources.
✗
A trunk native VLAN
Why it's wrong here
This is wrong because the symptom points to name resolution, not trunkVLAN behavior.
When this WOULD be correct
In a scenario where a question asks about VLAN configuration affecting inter-VLAN communication or switch port settings, a candidate might need to identify the correct native VLAN for trunk ports to ensure proper traffic flow between VLANs, making this option correct.
✗
An OSPF router ID
Why it's wrong here
This is wrong because end hosts do not need OSPF router IDs for name resolution.
When this WOULD be correct
If the question were about troubleshooting OSPF routing issues, such as a failure to establish neighbor relationships or route advertisement problems, then identifying the correct OSPF router ID would be crucial for proper network communication.
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.
✓A DNS server addressCorrect answer▾
Why this is correct
This is correct because the host needs DNS information to resolve hostnames.
✗A new MAC addressWrong answer — click to see why▾
Why this is wrong here
A MAC address is a hardware identifier used for local network communication at Layer 2, and it has no role in hostname resolution. Changing the MAC address would not affect the ability to resolve hostnames to IP addresses.
★ When this WOULD be the correct answer
In a question about a network security scenario where a device's MAC address has changed due to a network policy update, and the question asks about connectivity issues related to access control lists (ACLs) or MAC filtering, a new MAC address could be the correct answer if it is preventing access to certain resources.
Why candidates choose this
Students might confuse MAC addresses with IP addresses or think that network connectivity issues at Layer 2 could impact name resolution, but DNS operates at Layer 3 and above.
✗A trunk native VLANWrong answer — click to see why▾
Why this is wrong here
A trunk native VLAN is a configuration for switch ports that carry multiple VLANs, and it is unrelated to hostname resolution. The symptom described is a DNS issue, not a VLAN or trunking problem.
★ When this WOULD be the correct answer
In a scenario where a question asks about VLAN configuration affecting inter-VLAN communication or switch port settings, a candidate might need to identify the correct native VLAN for trunk ports to ensure proper traffic flow between VLANs, making this option correct.
Why candidates choose this
Test-takers might associate VLANs with network segmentation and think that misconfigurations could prevent hostname resolution, but DNS is a separate service that does not depend on VLAN settings.
✗An OSPF router IDWrong answer — click to see why▾
Why this is wrong here
OSPF router IDs are used by routers in OSPF routing protocol operations, not by end hosts. End hosts do not participate in OSPF and do not require a router ID for any function, including name resolution.
★ When this WOULD be the correct answer
If the question were about troubleshooting OSPF routing issues, such as a failure to establish neighbor relationships or route advertisement problems, then identifying the correct OSPF router ID would be crucial for proper network communication.
Why candidates choose this
Students might confuse OSPF with DNS or think that routing protocols are involved in name resolution, but DNS is an application-layer service independent of routing protocols.
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
Cisco often tests the distinction between Layer 3 connectivity (IP reachability) and application-layer services (DNS), so the trap here is that candidates might suspect a routing or switching issue (like a missing default gateway or VLAN mismatch) when the symptom clearly isolates the problem to name resolution.
Detailed technical explanation
How to think about this question
DNS resolution typically uses UDP port 53 for queries, and the host must have a configured DNS server (e.g., via DHCP or static assignment) to send these queries. If the DNS server is unreachable or not configured, the host's resolver library (e.g., gethostbyname() on Linux or DnsQuery on Windows) will fail, returning an error like 'Name or service not known'. In a real-world scenario, a misconfigured DHCP scope that omits the DNS server option (Option 6) is a common cause of this symptom.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Network Services and Security — This question tests Network Services and Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: A DNS server address — When a host can reach remote websites by IP address but not by hostname, the issue is that the host cannot resolve the hostname to an IP address. DNS (Domain Name System) is responsible for this resolution, and if the DNS server address is missing or misconfigured on the host, name resolution fails. This is the strongest suspect because all other network connectivity (routing, switching) is functional, as proven by successful IP-based access.
What should I do if I get this 200-301 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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