Question 217 of 2,152

Device Management →mediumMultiple ChoiceObjective-mapped

SNMP Traps Not Sending

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 sending SNMP traps to the NMS server at 10.1.1.100. The SNMP configuration includes 'snmp-server enable traps' and 'snmp-server host 10.1.1.100 version 2c public'. The engineer can ping the NMS server from the router, and 'show snmp' indicates SNMP is enabled. What is the most likely cause of the missing traps?

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 server is not listening on UDP port 162.
Why wrong: The NMS server is reachable via ping, but this does not confirm the SNMP trap receiver is listening; however, the more common cause on the router side is the missing trap-source.
B
The 'snmp-server trap-source' command is missing, causing traps to use an incorrect source IP.
Without 'snmp-server trap-source', the router uses the outgoing interface IP, which may not match the NMS's expected source or may be unreachable.
C
The SNMP community string 'public' is not configured on the router.
Why wrong: The community 'public' is configured in the 'snmp-server host' command, and 'show snmp' would show it; missing community would prevent responses to polls, not traps.
D
The router's ACL is blocking outbound UDP traffic to port 162.
Why wrong: While possible, the engineer can ping the NMS, and typically SNMP traps use UDP; an ACL blocking UDP 162 would be a less common default scenario.

Full breakdown with real-world context →

Quick Answer

The answer is a missing `snmp-server trap-source` command, which causes the router to source SNMP traps from an interface that may not be reachable or may present an incorrect source IP to the NMS server. Even with `snmp-server enable traps` and a properly configured host, the router selects the outgoing interface’s IP as the trap source by default; if that interface is not the one the NMS expects (e.g., a loopback or management interface), the NMS may drop or ignore the traps. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of SNMP trap delivery mechanics and the importance of explicit source-interface configuration, often appearing as a subtle troubleshooting trap where ping succeeds but traps fail. A common memory tip is “traps need a trusted source”—always verify that the trap-source matches the NMS’s expected IP, or use a loopback interface to ensure consistent reachability.

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 'snmp-server trap-source' command is missing, causing traps to use an incorrect source IP.

The most likely cause is that the 'snmp-server trap-source' command is missing. Without this command, the router uses the IP address of the outbound interface (e.g., a loopback or WAN interface) as the source for SNMP traps. If the NMS server expects traps from a specific source IP (e.g., the router's management IP), it may drop or ignore them, even though the router can ping the NMS. The 'show snmp' output confirms SNMP is enabled, and the ping test rules out basic reachability, pointing to a source IP mismatch as the root cause.

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 server is not listening on UDP port 162.
Why it's wrong here
The NMS server is reachable via ping, but this does not confirm the SNMP trap receiver is listening; however, the more common cause on the router side is the missing trap-source.
✓
The 'snmp-server trap-source' command is missing, causing traps to use an incorrect source IP.
Why this is correct
Without 'snmp-server trap-source', the router uses the outgoing interface IP, which may not match the NMS's expected source or may be unreachable.
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 SNMP community string 'public' is not configured on the router.
Why it's wrong here
The community 'public' is configured in the 'snmp-server host' command, and 'show snmp' would show it; missing community would prevent responses to polls, not traps.
✗
The router's ACL is blocking outbound UDP traffic to port 162.
Why it's wrong here
While possible, the engineer can ping the NMS, and typically SNMP traps use UDP; an ACL blocking UDP 162 would be a less common default scenario.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the 'snmp-server trap-source' command as a subtle but critical configuration requirement, leading candidates to overlook it and instead blame community strings or ACLs when basic connectivity (ping) is successful.

Trap categories for this question

Command / output trap
The community 'public' is configured in the 'snmp-server host' command, and 'show snmp' would show it; missing community would prevent responses to polls, not traps.
Scenario analysis trap
While possible, the engineer can ping the NMS, and typically SNMP traps use UDP; an ACL blocking UDP 162 would be a less common default scenario.

Detailed technical explanation

How to think about this question

SNMP traps are sent as UDP datagrams to port 162 on the NMS. The 'snmp-server trap-source' command forces the router to use a specific interface's IP as the source address in the trap packet. This is critical in environments with multiple interfaces (e.g., management, data, loopback) because the NMS may have ACLs or routing policies that only accept traps from a known management IP. Without it, the router uses the IP of the egress interface, which can change dynamically (e.g., via routing table changes) and cause traps to be dropped by the NMS or intermediate firewalls.

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.

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: The 'snmp-server trap-source' command is missing, causing traps to use an incorrect source IP. — The most likely cause is that the 'snmp-server trap-source' command is missing. Without this command, the router uses the IP address of the outbound interface (e.g., a loopback or WAN interface) as the source for SNMP traps. If the NMS server expects traps from a specific source IP (e.g., the router's management IP), it may drop or ignore them, even though the router can ping the NMS. The 'show snmp' output confirms SNMP is enabled, and the ping test rules out basic reachability, pointing to a source IP mismatch as the root cause.

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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