The answer is to remove the unreachable DNS server 192.0.2.53, add an A record for webserver.internal (192.168.10.50), and correct the PTR record for that IP to point to webserver.internal. This is correct because DNS resolution troubleshooting on Cisco routers hinges on three pillars: reachable name servers, complete forward mapping (A records), and consistent reverse mapping (PTR records). The unreachable server causes timeouts for external queries like 'example.com', while the missing A record triggers NXDOMAIN for internal hosts, and the mismatched PTR record breaks reverse lookups. On the CCNA 200-301 v2 exam, this scenario tests your ability to diagnose multi-layered DNS failures using commands like `nslookup` and `dig`, often appearing as a simulation where you must edit both global name-server lists and local host entries. A common trap is fixing only one issue—like adding the A record—while ignoring the unreachable server or the wrong PTR. Remember the three-check rule: servers reachable, forward exists, reverse matches.
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.
Exhibit
R1# show running-config | section ip domain
ip domain lookup
ip domain name internal
ip name-server 192.0.2.53
ip name-server 203.0.113.53
!
R1# show ip dns
DNS lookup enabled
Default domain: internal
Name-server list:
192.0.2.53 (unreachable)
203.0.113.53
R1# nslookup webserver.internal
Server: 203.0.113.53
Address: 203.0.113.53#53
** server can't find webserver.internal: NXDOMAIN
R1# nslookup 192.168.10.50
Server: 203.0.113.53
Address: 203.0.113.53#53
50.10.168.192.in-addr.arpa name = mail.internal.
R1# dig @203.0.113.53 example.com
; <<>> DiG 9.11.3 <<>> @203.0.113.53 example.com
;; connection timed out; no servers could be reached
You are connected to R1, a router that serves as the DNS resolver for the local network 192.168.10.0/24. Users report that they cannot resolve the hostname 'webserver.internal' to its IP address (192.168.10.50), and reverse DNS lookups for that IP return a different name. Additionally, some queries to an external domain 'example.com' time out. Diagnose and fix the DNS configuration on R1 using nslookup and dig commands where applicable, ensuring proper forward and reverse resolution for internal hosts and reachability to external DNS servers.
R1# show running-config | section ip domain
ip domain lookup
ip domain name internal
ip name-server 192.0.2.53
ip name-server 203.0.113.53
!
R1# show ip dns
DNS lookup enabled
Default domain: internal
Name-server list:
192.0.2.53 (unreachable)
203.0.113.53
R1# nslookup webserver.internal
Server: 203.0.113.53
Address: 203.0.113.53#53
** server can't find webserver.internal: NXDOMAIN
R1# nslookup 192.168.10.50
Server: 203.0.113.53
Address: 203.0.113.53#53
50.10.168.192.in-addr.arpa name = mail.internal.
R1# dig @203.0.113.53 example.com
; <<>> DiG 9.11.3 <<>> @203.0.113.53 example.com
;; connection timed out; no servers could be reached
A
Remove the unreachable DNS server 192.0.2.53, add an A record for webserver.internal (192.168.10.50), and correct the PTR record for 192.168.10.50 to point to webserver.internal.
This is correct because it addresses all three issues: the unreachable DNS server causes timeouts for external queries, the missing A record prevents forward resolution of webserver.internal, and the incorrect PTR record causes reverse DNS to return the wrong name. Removing or replacing the unreachable server restores external resolution, while adding the A record and fixing the PTR record ensures proper internal resolution.
B
Add an A record for webserver.internal (192.168.10.50) and correct the PTR record for 192.168.10.50 to point to webserver.internal, but leave the unreachable DNS server 192.0.2.53 in the configuration.
Why wrong: This is incorrect because leaving the unreachable DNS server 192.0.2.53 in the configuration will continue to cause timeouts for external queries like example.com. The router will attempt to query that server first or in parallel, leading to delays or failures.
C
Remove the unreachable DNS server 192.0.2.53 and add an A record for webserver.internal (192.168.10.50), but do not correct the PTR record for 192.168.10.50.
Why wrong: This is incorrect because while it fixes the external timeout and forward resolution, it leaves the reverse DNS mapping wrong. Reverse DNS lookups for 192.168.10.50 will still return 'mail.internal' instead of 'webserver.internal', which can cause issues with applications that rely on reverse lookups (e.g., SMTP, logging).
D
Replace the unreachable DNS server 192.0.2.53 with a reachable one, and correct the PTR record for 192.168.10.50 to point to webserver.internal, but do not add an A record for webserver.internal.
Why wrong: This is incorrect because without an A record for webserver.internal, forward DNS queries for that hostname will still fail (return NXDOMAIN). The PTR record alone does not enable forward resolution; both records are needed.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Remove the unreachable DNS server 192.0.2.53, add an A record for webserver.internal (192.168.10.50), and correct the PTR record for 192.168.10.50 to point to webserver.internal.
The DNS server 192.0.2.53 is unreachable, causing timeouts for external queries. The primary DNS server 203.0.113.53 returns NXDOMAIN for 'webserver.internal' because no A record exists for that hostname in the internal zone. Additionally, the PTR record for 192.168.10.50 incorrectly points to 'mail.internal' instead of 'webserver.internal'. To fix, first remove the unreachable DNS server with 'no ip name-server 192.0.2.53' or replace it with a reachable one. Then, on the DNS server (or via static host entries on R1), add an A record for webserver.internal (192.168.10.50) and correct the PTR record to point to webserver.internal. Optionally, configure 'ip host webserver.internal 192.168.10.50' on R1 for local resolution.
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.
✓
Remove the unreachable DNS server 192.0.2.53, add an A record for webserver.internal (192.168.10.50), and correct the PTR record for 192.168.10.50 to point to webserver.internal.
Why this is correct
This is correct because it addresses all three issues: the unreachable DNS server causes timeouts for external queries, the missing A record prevents forward resolution of webserver.internal, and the incorrect PTR record causes reverse DNS to return the wrong name. Removing or replacing the unreachable server restores external resolution, while adding the A record and fixing the PTR record ensures proper internal resolution.
Related concept
Read the scenario before looking for a memorised answer.
✗
Add an A record for webserver.internal (192.168.10.50) and correct the PTR record for 192.168.10.50 to point to webserver.internal, but leave the unreachable DNS server 192.0.2.53 in the configuration.
Why it's wrong here
This is incorrect because leaving the unreachable DNS server 192.0.2.53 in the configuration will continue to cause timeouts for external queries like example.com. The router will attempt to query that server first or in parallel, leading to delays or failures.
✗
Remove the unreachable DNS server 192.0.2.53 and add an A record for webserver.internal (192.168.10.50), but do not correct the PTR record for 192.168.10.50.
Why it's wrong here
This is incorrect because while it fixes the external timeout and forward resolution, it leaves the reverse DNS mapping wrong. Reverse DNS lookups for 192.168.10.50 will still return 'mail.internal' instead of 'webserver.internal', which can cause issues with applications that rely on reverse lookups (e.g., SMTP, logging).
✗
Replace the unreachable DNS server 192.0.2.53 with a reachable one, and correct the PTR record for 192.168.10.50 to point to webserver.internal, but do not add an A record for webserver.internal.
Why it's wrong here
This is incorrect because without an A record for webserver.internal, forward DNS queries for that hostname will still fail (return NXDOMAIN). The PTR record alone does not enable forward resolution; both records are needed.
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.
✓Remove the unreachable DNS server 192.0.2.53, add an A record for webserver.internal (192.168.10.50), and correct the PTR record for 192.168.10.50 to point to webserver.internal.Correct answer▾
Why this is correct
This is correct because it addresses all three issues: the unreachable DNS server causes timeouts for external queries, the missing A record prevents forward resolution of webserver.internal, and the incorrect PTR record causes reverse DNS to return the wrong name. Removing or replacing the unreachable server restores external resolution, while adding the A record and fixing the PTR record ensures proper internal resolution.
✗Add an A record for webserver.internal (192.168.10.50) and correct the PTR record for 192.168.10.50 to point to webserver.internal, but leave the unreachable DNS server 192.0.2.53 in the configuration.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that an unreachable DNS server must be removed or replaced to resolve external queries; simply fixing internal records does not address the timeout issue.
Why candidates choose this
Candidates might think that fixing the internal records is sufficient and overlook the external server issue, or they may assume the router will automatically skip the unreachable server.
✗Remove the unreachable DNS server 192.0.2.53 and add an A record for webserver.internal (192.168.10.50), but do not correct the PTR record for 192.168.10.50.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that reverse DNS must match the forward record for consistency; an incorrect PTR record is a problem even if forward resolution works.
Why candidates choose this
Candidates might think reverse DNS is less important or that the PTR record is automatically updated when an A record is added, which is not true.
✗Replace the unreachable DNS server 192.0.2.53 with a reachable one, and correct the PTR record for 192.168.10.50 to point to webserver.internal, but do not add an A record for webserver.internal.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that forward and reverse DNS are independent; adding a PTR record does not create an A record. The A record must exist for forward queries to succeed.
Why candidates choose this
Candidates might assume that fixing the PTR record also creates the A record, or that reverse DNS is sufficient for name resolution, which is a common misconception.
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
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 practitioner preparing for the 200-301 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Identify which 200-301 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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: Remove the unreachable DNS server 192.0.2.53, add an A record for webserver.internal (192.168.10.50), and correct the PTR record for 192.168.10.50 to point to webserver.internal. — The DNS server 192.0.2.53 is unreachable, causing timeouts for external queries. The primary DNS server 203.0.113.53 returns NXDOMAIN for 'webserver.internal' because no A record exists for that hostname in the internal zone. Additionally, the PTR record for 192.168.10.50 incorrectly points to 'mail.internal' instead of 'webserver.internal'. To fix, first remove the unreachable DNS server with 'no ip name-server 192.0.2.53' or replace it with a reachable one. Then, on the DNS server (or via static host entries on R1), add an A record for webserver.internal (192.168.10.50) and correct the PTR record to point to webserver.internal. Optionally, configure 'ip host webserver.internal 192.168.10.50' on R1 for local resolution.
What should I do if I get this 200-301 question wrong?
Identify which 200-301 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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