Question 1,797 of 2,152

Device Management →mediumMultiple ChoiceObjective-mapped

SNMP Poll Not Responding Due to Community ACL

This 300-410 practice question tests your understanding of device management. 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 network engineer is troubleshooting a router that is not responding to SNMP polls from the NMS at 10.1.1.100. The SNMP configuration includes 'snmp-server community public RO' and 'snmp-server community private RW'. The engineer can ping the router from the NMS. 'show snmp' shows SNMP is enabled. What is the most likely cause?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The NMS is using the wrong SNMP version.
Why wrong: The router supports SNMPv2c by default; if the NMS uses SNMPv1, it would still work with the community string. Version mismatch is less common than ACL filtering.
B
An ACL is applied to the SNMP community that denies the NMS IP.
The configuration may include 'snmp-server community public RO 10', where ACL 10 denies the NMS; this is a common misconfiguration.
C
The router's SNMP agent is disabled due to high CPU.
Why wrong: High CPU would not disable SNMP; the agent would still respond, albeit slowly.
D
The NMS is using the wrong community string.
Why wrong: While possible, the engineer has verified the configuration; the community strings are correct, so the issue is likely access control.

Full breakdown with real-world context →

Quick Answer

The answer is an ACL applied to the SNMP community that denies the NMS IP. This is correct because even when SNMP communities like "public" and "private" are configured and the router responds to pings, an access-list attached to the community string can silently drop SNMP requests from unauthorized sources, causing the poll to fail while leaving other connectivity intact. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of SNMP security features and the common misconfiguration where an ACL is applied to a community without permitting the NMS IP—a frequent trap because engineers often check basic SNMP enablement and reachability first. Remember that a successful ping only confirms IP connectivity, not SNMP access; the ACL acts as a filter at the application layer. Memory tip: "Ping works, SNMP doesn't? Check the community ACL—it's the silent gatekeeper."

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

✓

An ACL is applied to the SNMP community that denies the NMS IP.

The NMS can ping the router, confirming IP reachability, and 'show snmp' confirms SNMP is enabled. The most likely cause is an ACL applied to the SNMP community that denies the NMS IP address (10.1.1.100). Cisco IOS allows an access-list to be attached to an SNMP community string using the 'snmp-server community <string> [RO|RW] <acl-number>' command, which filters SNMP requests based on source IP. Since the NMS can ping but not poll, the ACL is blocking SNMP traffic while permitting ICMP.

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.

✗
The NMS is using the wrong SNMP version.
Why it's wrong here
The router supports SNMPv2c by default; if the NMS uses SNMPv1, it would still work with the community string. Version mismatch is less common than ACL filtering.
✓
An ACL is applied to the SNMP community that denies the NMS IP.
Why this is correct
The configuration may include 'snmp-server community public RO 10', where ACL 10 denies the NMS; this is a common misconfiguration.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The router's SNMP agent is disabled due to high CPU.
Why it's wrong here
High CPU would not disable SNMP; the agent would still respond, albeit slowly.
✗
The NMS is using the wrong community string.
Why it's wrong here
While possible, the engineer has verified the configuration; the community strings are correct, so the issue is likely access control.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the distinction between reachability (ping working) and SNMP-specific filtering (ACL on community), leading candidates to incorrectly blame community string mismatch or SNMP version when the real issue is an access-list silently dropping SNMP packets.

Detailed technical explanation

How to think about this question

When an ACL is applied to an SNMP community, the router checks the source IP of incoming SNMP packets against the ACL before processing the request; if denied, the router silently drops the packet without sending an SNMP error response, which explains why the NMS sees no response. This behavior differs from a community string mismatch, where the router would send an SNMP message with error-status 'noSuchName' (for SNMPv1) or 'authorizationError' (for SNMPv2c). In real-world scenarios, engineers often forget that ACLs applied to SNMP communities also affect SNMP traps and informs sent from the router, not just polls.

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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

Visual reference

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 300-410 question test?

Device Management — This question tests Device Management — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: An ACL is applied to the SNMP community that denies the NMS IP. — The NMS can ping the router, confirming IP reachability, and 'show snmp' confirms SNMP is enabled. The most likely cause is an ACL applied to the SNMP community that denies the NMS IP address (10.1.1.100). Cisco IOS allows an access-list to be attached to an SNMP community string using the 'snmp-server community <string> [RO|RW] <acl-number>' command, which filters SNMP requests based on source IP. Since the NMS can ping but not poll, the ACL is blocking SNMP traffic while permitting ICMP.

What should I do if I get this 300-410 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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