CCNA Network Services and Security Practice Question
Exhibit
VLAN 70 DHCP scope: network 10.70.70.0 255.255.255.0 default-router 10.70.70.1 Client tests: - ping 192.0.2.50 = success - open http://192.0.2.50 = success - open http://portal.branch.lab = fail
Based on the exhibit, why are clients in VLAN 70 failing to resolve hostnames even though they can reach remote IP addresses?
⚠ Common exam trap
A frequent exam trap is to mistake the inability to resolve hostnames as a routing or VLAN trunking problem. Candidates might incorrectly believe that removing the default gateway or converting the VLAN to the native VLAN on trunks will resolve the issue. However, these options do not address DNS resolution, which is an application-layer service independent of Layer 3 forwarding. The trap arises because clients can reach remote IP addresses, misleading candidates to focus on routing or VLAN configuration rather than missing DNS server information in the DHCP scope.
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
✓
The clients are missing valid DNS server information.
The strongest explanation is that the clients are missing valid DNS server information. In practical terms, successful reachability to remote IP addresses proves that Layer 3 forwarding is working. The failure occurs only when a hostname is used, which points to a naming service problem rather than a general connectivity problem. The DHCP scope shown provides an address and default gateway, but no DNS server option is defined. This is a very realistic IP-services troubleshooting pattern because the network path works while application usability still fails.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The clients are missing valid DNS server information.
Why this is correct
The DHCP scope assigns IP configuration but does not include Option 6 (DNS server), so clients receive no resolver address. When a user pings a hostname, the client cannot query a DNS server, causing resolution failure; direct IP access works because no DNS is required. This exactly matches the exhibited symptom of IP connectivity succeeding while hostname-based access fails.
- ✗
The default gateway must be removed from the DHCP scope.
Why it's wrong here
Removing the default gateway from the DHCP scope would eliminate the router as the next hop, breaking all off-subnet communication. The problem is isolated to hostname resolution while IP connectivity succeeds, so a missing gateway would cause total network failure, not just DNS failure. Therefore, the default gateway must remain in the scope and cannot be the cause.
When this WOULD be correct
In a different scenario, if a question specified that clients were unable to communicate with any external networks due to misconfigured DHCP settings, and the default gateway was indeed incorrectly set, then removing it could be the correct action to restore connectivity.
- ✗
The clients must use PPP before DNS works.
Why it's wrong here
PPP (Point-to-Point Protocol) is a WAN data-link encapsulation used on serial or DSL links, not a service required for DNS on an Ethernet LAN. DNS resolution operates over IP and is independent of the data-link protocol; clients do not need PPP to send DNS queries. This option incorrectly conflates a WAN technology with local DHCP operation and is unrelated to the VLAN 70 issue.
When this WOULD be correct
In a scenario where the question specifies that clients are connecting over a PPP link and that DNS resolution is dependent on the successful establishment of a PPP connection, this option would be correct. For instance, if the question stated that clients can only access DNS after establishing a PPP connection, then this would apply.
- ✗
The VLAN must be converted to the native VLAN on all trunks.
Why it's wrong here
The native VLAN in 802.1Q trunks carries untagged frames; changing VLAN 70 to native would affect trunk tagging and could cause broadcast or misdelivery issues. However, the symptom is specifically that clients reach services by IP but not by hostname, indicating a DNS problem, not a Layer 2 forwarding issue. If the native VLAN were misconfigured, general connectivity would fail, not just name resolution.
When this WOULD be correct
In a different exam scenario, if the question asked about issues related to VLAN tagging and inter-VLAN communication where the native VLAN configuration was misconfigured, then this option could be correct if it led to traffic being untagged and not reaching the correct destination for DNS queries.
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.
✓The clients are missing valid DNS server information.Correct answer▾
Why this is correct
The DHCP scope assigns IP configuration but does not include Option 6 (DNS server), so clients receive no resolver address. When a user pings a hostname, the client cannot query a DNS server, causing resolution failure; direct IP access works because no DNS is required. This exactly matches the exhibited symptom of IP connectivity succeeding while hostname-based access fails.
✗The default gateway must be removed from the DHCP scope.Wrong answer — click to see why▾
Why this is wrong here
The default gateway is essential for clients to communicate outside their subnet, and removing it would break all remote access, not just hostname resolution. Since clients can reach remote IPs, the gateway is correctly configured.
★ When this WOULD be the correct answer
In a different scenario, if a question specified that clients were unable to communicate with any external networks due to misconfigured DHCP settings, and the default gateway was indeed incorrectly set, then removing it could be the correct action to restore connectivity.
Why candidates choose this
Students might confuse the default gateway with DNS, thinking that removing it could force clients to use alternative name resolution methods, but this is incorrect as the gateway is required for routing.
✗The clients must use PPP before DNS works.Wrong answer — click to see why▾
Why this is wrong here
PPP (Point-to-Point Protocol) is used for serial links and is unrelated to DNS resolution in a typical Ethernet LAN environment. DNS works over IP and does not require PPP.
★ When this WOULD be the correct answer
In a scenario where the question specifies that clients are connecting over a PPP link and that DNS resolution is dependent on the successful establishment of a PPP connection, this option would be correct. For instance, if the question stated that clients can only access DNS after establishing a PPP connection, then this would apply.
Why candidates choose this
Test-takers might associate PPP with dial-up or WAN connections where DNS might be negotiated, but in a LAN scenario, PPP is irrelevant.
✗The VLAN must be converted to the native VLAN on all trunks.Wrong answer — click to see why▾
Why this is wrong here
The native VLAN is used for untagged traffic on trunk links and does not affect DNS resolution. Changing a VLAN to native would not fix hostname resolution issues, as the problem is at the application layer (DNS), not layer 2.
★ When this WOULD be the correct answer
In a different exam scenario, if the question asked about issues related to VLAN tagging and inter-VLAN communication where the native VLAN configuration was misconfigured, then this option could be correct if it led to traffic being untagged and not reaching the correct destination for DNS queries.
Why candidates choose this
Students might think that VLAN configuration issues can cause all communication problems, but the symptom of working IP access but failing hostname resolution points specifically to DNS, not VLAN misconfiguration.
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?”
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.