The answer is to configure R1 as a local DNS server with an A record for server1.example.com (192.168.1.10) and a PTR record for 192.168.1.10, then remove the unreachable forwarder 192.0.2.53. This resolves the dual failure: the DNS forwarder unreachable error causes forward lookups to return NXDOMAIN because R1 cannot reach the external server, while the missing PTR record breaks reverse DNS queries for the internal subnet. On the CCNA 200-301 v2 exam, this tests your understanding of how Cisco devices handle DNS resolution—specifically that a forwarder failure does not automatically fall back to local records unless explicitly configured. A common trap is assuming a forwarder is optional; in fact, if it is unreachable, all lookups fail unless you remove it or point to a reachable server. Remember: forwarder unreachable equals NXDOMAIN, and no PTR equals reverse failure—fix both by making the switch its own authoritative server. Memory tip: “No forward, no reverse—local records break the curse.”
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.
Network Topology
You are connected to R1, a multilayer switch acting as a DNS client and DNS server for the local network. The network uses 192.168.1.0/24 for internal hosts. Users report that hostnames like 'server1.example.com' fail to resolve. Diagnose and fix the DNS resolution issue using nslookup and dig. Ensure that R1 can resolve both forward and reverse DNS queries correctly.
R1# show running-config | section ip domain
ip domain lookup
ip domain name example.com
ip name-server 192.0.2.53
!
R1# show ip dns server
DNS server is enabled
Forwarding: enabled
Forwarder: 192.0.2.53 (unreachable)
R1# nslookup server1.example.com
Server: 192.0.2.53
Address: 192.0.2.53#53
** server can't find server1.example.com: NXDOMAIN
R1# dig -x 192.168.1.10
; <<>> DiG 9.11.4-P1 <<>> -x 192.168.1.10
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 12345
;; QUESTION SECTION:
;10.1.168.192.in-addr.arpa. IN PTR
;; AUTHORITY SECTION:
0.in-addr.arpa. 86400 IN SOA ns.example.com. admin.example.com. 1 3600 900 604800 86400
;; Query time: 1 msec
;; SERVER: 192.0.2.53#53(192.0.2.53)
;; WHEN: Mon Jan 15 10:00:00 UTC 2024
;; MSG SIZE rcvd: 96
A
Configure R1 as a local DNS server with an A record for server1.example.com (192.168.1.10) and a PTR record for 192.168.1.10, then remove the unreachable forwarder 192.0.2.53 and ensure ip domain lookup uses the local server.
This resolves both issues: the forward lookup fails because the forwarder is unreachable, so using a local server with an A record fixes forward resolution; the reverse lookup fails due to missing PTR record, so adding one fixes reverse resolution. Removing the unreachable forwarder ensures queries go to the local server.
B
Configure R1 as a DNS server with only an A record for server1.example.com (192.168.1.10) and keep the forwarder 192.0.2.53 for other queries.
Why wrong: This is incorrect because the forwarder is unreachable, so forward queries will still fail. Additionally, no PTR record is added, so reverse lookups will still fail.
C
Remove the forwarder 192.0.2.53 and configure R1 as a DNS server with only a PTR record for 192.168.1.10.
Why wrong: This is incorrect because while removing the unreachable forwarder helps, without an A record for server1.example.com, forward lookups will still fail. Reverse lookups will work with the PTR record, but forward resolution remains broken.
D
Change the DNS forwarder to a reachable server like 8.8.8.8 and add a PTR record for 192.168.1.10 on R1.
Why wrong: This is incorrect because while changing the forwarder to a reachable server fixes forward lookups, the reverse lookup still requires a PTR record on the local server. However, the question implies R1 should act as a local DNS server, not rely on external forwarders for internal hostnames.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure R1 as a local DNS server with an A record for server1.example.com (192.168.1.10) and a PTR record for 192.168.1.10, then remove the unreachable forwarder 192.0.2.53 and ensure ip domain lookup uses the local server.
The issue is twofold: first, the DNS forwarder (192.0.2.53) is unreachable, causing forward lookups to fail with NXDOMAIN; second, there is no PTR record for the reverse lookup zone. The forward lookup failure is because R1 is configured to use an unreachable external DNS server. The reverse lookup failure is because no PTR record exists for the host IP. To fix, either configure a reachable DNS forwarder or enable local DNS server with appropriate records. Here, we configure R1 as a local DNS server with an A record for 'server1.example.com' pointing to 192.168.1.10 and a PTR record for the reverse lookup. Then we remove the unreachable forwarder and ensure ip domain lookup uses local server.
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.
✓
Configure R1 as a local DNS server with an A record for server1.example.com (192.168.1.10) and a PTR record for 192.168.1.10, then remove the unreachable forwarder 192.0.2.53 and ensure ip domain lookup uses the local server.
Why this is correct
This resolves both issues: the forward lookup fails because the forwarder is unreachable, so using a local server with an A record fixes forward resolution; the reverse lookup fails due to missing PTR record, so adding one fixes reverse resolution. Removing the unreachable forwarder ensures queries go to the local server.
Related concept
Read the scenario before looking for a memorised answer.
✗
Configure R1 as a DNS server with only an A record for server1.example.com (192.168.1.10) and keep the forwarder 192.0.2.53 for other queries.
Why it's wrong here
This is incorrect because the forwarder is unreachable, so forward queries will still fail. Additionally, no PTR record is added, so reverse lookups will still fail.
✗
Remove the forwarder 192.0.2.53 and configure R1 as a DNS server with only a PTR record for 192.168.1.10.
Why it's wrong here
This is incorrect because while removing the unreachable forwarder helps, without an A record for server1.example.com, forward lookups will still fail. Reverse lookups will work with the PTR record, but forward resolution remains broken.
✗
Change the DNS forwarder to a reachable server like 8.8.8.8 and add a PTR record for 192.168.1.10 on R1.
Why it's wrong here
This is incorrect because while changing the forwarder to a reachable server fixes forward lookups, the reverse lookup still requires a PTR record on the local server. However, the question implies R1 should act as a local DNS server, not rely on external forwarders for internal hostnames.
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.
✓Configure R1 as a local DNS server with an A record for server1.example.com (192.168.1.10) and a PTR record for 192.168.1.10, then remove the unreachable forwarder 192.0.2.53 and ensure ip domain lookup uses the local server.Correct answer▾
Why this is correct
This resolves both issues: the forward lookup fails because the forwarder is unreachable, so using a local server with an A record fixes forward resolution; the reverse lookup fails due to missing PTR record, so adding one fixes reverse resolution. Removing the unreachable forwarder ensures queries go to the local server.
✗Configure R1 as a DNS server with only an A record for server1.example.com (192.168.1.10) and keep the forwarder 192.0.2.53 for other queries.Wrong answer — click to see why▾
Why this is wrong here
The forwarder is unreachable, so keeping it will cause forward lookups to fail. Also, reverse lookup requires a PTR record, which is missing.
Why candidates choose this
Candidates may think that adding an A record alone is sufficient and that the forwarder can be kept for other queries, not realizing the forwarder is unreachable.
✗Remove the forwarder 192.0.2.53 and configure R1 as a DNS server with only a PTR record for 192.168.1.10.Wrong answer — click to see why▾
Why this is wrong here
Forward lookups require an A record mapping the hostname to an IP address; without it, forward queries return NXDOMAIN.
Why candidates choose this
Candidates may focus only on the reverse lookup issue mentioned in the problem and forget that forward lookups also fail due to the unreachable forwarder.
✗Change the DNS forwarder to a reachable server like 8.8.8.8 and add a PTR record for 192.168.1.10 on R1.Wrong answer — click to see why▾
Why this is wrong here
The scenario expects R1 to be a local DNS server for internal hosts; using an external forwarder for internal hostnames is not best practice and may not resolve internal names if the forwarder doesn't have the records.
Why candidates choose this
Candidates may think that using a public DNS server like 8.8.8.8 is a quick fix for forward lookups, but they overlook the requirement for local resolution and reverse lookup.
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: Configure R1 as a local DNS server with an A record for server1.example.com (192.168.1.10) and a PTR record for 192.168.1.10, then remove the unreachable forwarder 192.0.2.53 and ensure ip domain lookup uses the local server. — The issue is twofold: first, the DNS forwarder (192.0.2.53) is unreachable, causing forward lookups to fail with NXDOMAIN; second, there is no PTR record for the reverse lookup zone. The forward lookup failure is because R1 is configured to use an unreachable external DNS server. The reverse lookup failure is because no PTR record exists for the host IP. To fix, either configure a reachable DNS forwarder or enable local DNS server with appropriate records. Here, we configure R1 as a local DNS server with an A record for 'server1.example.com' pointing to 192.168.1.10 and a PTR record for the reverse lookup. Then we remove the unreachable forwarder and ensure ip domain lookup uses local server.
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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