Question 44 of 2,152

SNMP Troubleshooting →hardMultiple ChoiceObjective-mapped

SNMP Multiple Communities — First NMS Loses Access

This 300-410 practice question tests your understanding of snmp troubleshooting. 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.

An engineer configures SNMPv2c with a community string 'public' and an ACL that permits only the NMS IP address. The NMS can poll the router successfully. Later, the engineer adds a second community string 'monitor' with a different ACL that permits a second NMS. The first NMS now fails to poll. Which is the most likely explanation?

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.
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 ACL for the 'public' community string was accidentally removed when the 'monitor' community string was added.
If the engineer used the 'no snmp-server community public' command to reconfigure, the ACL might have been removed; the new configuration might not include the ACL, allowing all IPs or none.
B
The second community string 'monitor' has a higher priority and overrides the first.
Why wrong: Community strings are independent; the router matches the community string in the request.
C
The router can only support one community string at a time.
Why wrong: Routers support multiple community strings.
D
The first NMS must be reconfigured to use the 'monitor' community string.
Why wrong: The first NMS can continue to use 'public' if it is still configured.

Full breakdown with real-world context →

Quick Answer

The answer is that the ACL for the 'public' community string was accidentally removed when the 'monitor' community string was added. This is the most likely explanation because SNMPv2c relies on per-community ACLs to control access; when you configure a second community string, the router does not merge or overwrite existing ACLs unless the configuration command explicitly replaces the entire community entry. In the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how SNMP multiple communities break access when a configuration change inadvertently drops a previously applied ACL, a common trap where candidates assume the first NMS should still work based on the community string alone. The key insight is that each community string is an independent access control point, and the router checks the ACL associated with the received community string, not a combined list. Memory tip: "Each community gets its own bouncer—if you swap out the bouncer for 'public', the old guest gets turned away."

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 ACL for the 'public' community string was accidentally removed when the 'monitor' community string was added.

The most likely explanation is that when the engineer added the second community string 'monitor' with its associated ACL, the configuration command for the 'public' community string was accidentally overwritten or removed. In Cisco IOS, SNMP community strings are configured individually, and if the engineer used a command like `snmp-server community public RO` without reapplying the ACL, or if the ACL itself was modified or removed, the first NMS would lose access. Since the NMS could poll successfully before the change, the failure afterward points to a configuration error during the addition of the second community string.

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 ACL for the 'public' community string was accidentally removed when the 'monitor' community string was added.
Why this is correct
If the engineer used the 'no snmp-server community public' command to reconfigure, the ACL might have been removed; the new configuration might not include the ACL, allowing all IPs or none.
Clue confirmation
The clue words "first", "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The second community string 'monitor' has a higher priority and overrides the first.
Why it's wrong here
Community strings are independent; the router matches the community string in the request.
✗
The router can only support one community string at a time.
Why it's wrong here
Routers support multiple community strings.
✗
The first NMS must be reconfigured to use the 'monitor' community string.
Why it's wrong here
The first NMS can continue to use 'public' if it is still configured.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates may assume SNMP community strings have a priority or that only one can be active, but Cisco tests the understanding that multiple community strings can coexist and that a configuration mistake—like omitting the ACL when re-entering the community string—is the typical cause of such failures.

Detailed technical explanation

How to think about this question

Under the hood, SNMPv2c uses community strings as a form of 'password' for read or read-write access, and each community string can be tied to an ACL via the `snmp-server community <string> [view <view-name>] [ro|rw] [<acl-number-or-name>]` command. If the ACL referenced by the 'public' community string is deleted or modified to deny the first NMS, or if the community string itself is removed (e.g., by re-entering the command without the ACL), the first NMS will lose access. A common real-world scenario is when an engineer copies a configuration snippet that omits the ACL, inadvertently overwriting the existing community string entry.

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?

SNMP Troubleshooting — This question tests SNMP Troubleshooting — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The ACL for the 'public' community string was accidentally removed when the 'monitor' community string was added. — The most likely explanation is that when the engineer added the second community string 'monitor' with its associated ACL, the configuration command for the 'public' community string was accidentally overwritten or removed. In Cisco IOS, SNMP community strings are configured individually, and if the engineer used a command like `snmp-server community public RO` without reapplying the ACL, or if the ACL itself was modified or removed, the first NMS would lose access. Since the NMS could poll successfully before the change, the failure afterward points to a configuration error during the addition of the second community string.

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: "first", "most likely". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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