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. A key principle to apply: dNS translates human-readable hostnames into IP addresses, enabling network devices to locate resources using names instead of numeric IPs.. 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 user can reach a remote web server by IP address but not by hostname. Which service should be checked first?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
DNS
This is correct because DNS is responsible for resolving hostnames into IP information.
STP
Why wrong: This is wrong because spanning-tree does not provide hostname resolution.
PAT
Why wrong: This is wrong because NAT issues would typically affect IP connectivity more broadly, not just name resolution.
Port security
Why wrong: This is wrong because port security does not resolve hostnames.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
DNS
DNS should be checked first. In plain language, the path to the server appears to work because the user can reach it by numeric address. The missing function is the translation from hostname to IP-related information, and that is exactly what DNS provides. This is one of the clearest service-troubleshooting patterns in networking. If IP works but the name fails, DNS becomes the strongest first suspect. The correct answer is therefore the name-resolution service rather than a routing or switching feature.
Key principle: DNS translates human-readable hostnames into IP addresses, enabling network devices to locate resources using names instead of numeric IPs.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
DNS
Why this is correct
This is correct because DNS is responsible for resolving hostnames into IP information.
Clue confirmation
The clue word "first" in the question point toward this answer.
STP
Why it's wrong here
This is wrong because spanning-tree does not provide hostname resolution.
When this WOULD be correct
If the question were about a network topology issue where a switch is misconfigured and causing broadcast storms, leading to connectivity problems, then checking STP would be appropriate to ensure that the network topology is stable and loops are not affecting communication.
PAT
Why it's wrong here
This is wrong because NAT issues would typically affect IP connectivity more broadly, not just name resolution.
When this WOULD be correct
If the exam question stated that users could not access a web server by its public IP address but could access it by hostname, then PAT would be relevant. In this scenario, the question would focus on translating the public IP to the correct internal address, making PAT the correct answer.
Port security
Why it's wrong here
This is wrong because port security does not resolve hostnames.
When this WOULD be correct
If the question were about a scenario where a user is unable to connect to a network device due to unauthorized MAC addresses being blocked by port security, then checking port security settings would be the correct approach to diagnose the issue.
Option-by-option analysis
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.
Why this is correct
This is correct because DNS is responsible for resolving hostnames into IP information.
Why this is wrong here
STP (Spanning Tree Protocol) is used for preventing loops in Ethernet networks and does not relate to hostname resolution issues. Since the problem involves accessing a server by hostname, STP is not relevant.
★ When this WOULD be the correct answer
If the question were about a network topology issue where a switch is misconfigured and causing broadcast storms, leading to connectivity problems, then checking STP would be appropriate to ensure that the network topology is stable and loops are not affecting communication.
Why candidates choose this
Candidates may confuse STP with general network connectivity issues, thinking that any network protocol might be relevant when troubleshooting access problems, leading them to select this option without fully understanding the specific context of hostname resolution.
Why this is wrong here
PAT (Port Address Translation) is used for translating private IP addresses to a public IP address, allowing multiple devices on a local network to share a single public IP. It does not directly relate to hostname resolution issues, which are typically handled by DNS.
★ When this WOULD be the correct answer
If the exam question stated that users could not access a web server by its public IP address but could access it by hostname, then PAT would be relevant. In this scenario, the question would focus on translating the public IP to the correct internal address, making PAT the correct answer.
Why candidates choose this
Candidates might choose PAT due to a misunderstanding of network address translation concepts, thinking that any connectivity issue involving IP addresses could be related to address translation mechanisms.
Why this is wrong here
Port security is a feature used to restrict access to a switch port based on MAC addresses, and it does not directly affect the resolution of hostnames to IP addresses. Therefore, it is not relevant when a user can reach a server by IP but not by hostname.
★ When this WOULD be the correct answer
If the question were about a scenario where a user is unable to connect to a network device due to unauthorized MAC addresses being blocked by port security, then checking port security settings would be the correct approach to diagnose the issue.
Why candidates choose this
Candidates may confuse port security with network access issues, thinking that if a user cannot access a resource, it might be due to security settings on the switch, leading them to select this option.
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
A frequent exam trap is selecting PAT or STP as the cause when a user cannot reach a server by hostname but can by IP address. Candidates may mistakenly associate PAT with all IP-related issues, but PAT only translates IP addresses and ports for outbound traffic and does not resolve hostnames. Similarly, STP manages Layer 2 loop prevention and does not affect Layer 3 name resolution. Confusing these services with DNS leads to incorrect troubleshooting steps. The key is to recognize that DNS is the only service responsible for translating hostnames to IP addresses, so it must be checked first when name resolution fails but IP connectivity succeeds.
Detailed technical explanation
The Domain Name System (DNS) is a fundamental IP service that translates human-readable hostnames into IP addresses, enabling users and applications to locate resources on a network or the internet. When a user enters a hostname, the DNS client queries a DNS server to resolve that name into its corresponding IP address. This process is essential because network communication relies on IP addresses, not hostnames. Cisco devices and networks depend heavily on DNS for name resolution, especially in environments where users or systems access resources by name rather than by numeric IP. In troubleshooting connectivity issues where a user can reach a remote server by IP address but not by hostname, the first step is to verify the DNS service. This is because successful IP connectivity confirms that routing and switching functions are operational, and the problem lies specifically in the name resolution process. Cisco IOS devices use DNS settings configured via commands such as 'ip name-server' to specify DNS servers. If DNS is misconfigured, unreachable, or the DNS server lacks the correct records, hostname resolution will fail, causing access issues despite valid IP connectivity. A common exam trap is to confuse DNS issues with other network services like NAT or spanning-tree. For example, PAT (Port Address Translation) affects IP address translation but does not impact hostname resolution directly. Similarly, STP (Spanning Tree Protocol) manages Layer 2 loop prevention and does not influence DNS. Understanding that DNS operates at the application layer and is responsible solely for name-to-IP mapping helps avoid misdiagnosis. In practical Cisco networking, ensuring DNS servers are reachable and correctly configured is critical for seamless hostname-based access.
Key takeaway
DNS translates human-readable hostnames into IP addresses, enabling network devices to locate resources using names instead of numeric IPs.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Review dNS translates human-readable hostnames into IP addresses, enabling network devices to locate resources using names instead of numeric IPs., then practise related 200-301 questions on the same topic to reinforce the concept.
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FAQ
Network Services and Security — This question tests Network Services and Security — DNS translates human-readable hostnames into IP addresses, enabling network devices to locate resources using names instead of numeric IPs..
The correct answer is: DNS — DNS should be checked first. In plain language, the path to the server appears to work because the user can reach it by numeric address. The missing function is the translation from hostname to IP-related information, and that is exactly what DNS provides. This is one of the clearest service-troubleshooting patterns in networking. If IP works but the name fails, DNS becomes the strongest first suspect. The correct answer is therefore the name-resolution service rather than a routing or switching feature.
Review dNS translates human-readable hostnames into IP addresses, enabling network devices to locate resources using names instead of numeric IPs., then practise related 200-301 questions on the same topic to reinforce the concept.
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
DNS translates human-readable hostnames into IP addresses, enabling network devices to locate resources using names instead of numeric IPs.
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Last reviewed: May 17, 2026
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