The answer is that the CoPP policy’s ACL does not include the NMS IP address, so SNMP packets from the NMS are dropped by the class-default. CoPP applies to control plane traffic, meaning any SNMP polling reaching the router’s control plane must match a permit entry in the CoPP class map; if the ACL is misconfigured or missing the NMS source, the traffic falls into class-default, which typically drops all unmatched packets. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding that CoPP operates independently from SNMP’s own ACL—a common trap is assuming the SNMP community-string ACL alone protects the NMS, but CoPP can override it. Remember the memory tip: “CoPP is the bouncer; if the bouncer’s list is wrong, even VIPs get turned away.” Always verify that the CoPP ACL explicitly permits the NMS source IP, and check the class-default action to avoid silent drops.
300-410 SNMP Troubleshooting Practice Question
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 the NMS. The NMS can poll the router. The engineer then applies a CoPP policy that drops SNMP packets (UDP port 161) from all sources except the NMS. The 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: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
The CoPP policy's ACL does not include the NMS IP address, so SNMP packets from the NMS are dropped by the class-default.
CoPP policies typically have a class that matches traffic to be permitted; if the NMS is not matched, its packets fall into class-default, which may be set to drop.
B
CoPP only affects routing protocol traffic, not SNMP.
Why wrong: CoPP can filter any control plane traffic, including SNMP.
C
The SNMP community string ACL is overridden by the CoPP policy.
Why wrong: The community string ACL and CoPP are independent; both must permit the traffic.
D
The router requires a reload for the CoPP policy to take effect.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The CoPP policy's ACL does not include the NMS IP address, so SNMP packets from the NMS are dropped by the class-default.
CoPP applies to control plane traffic. If the CoPP policy is misconfigured, it may drop SNMP packets even from permitted sources. Additionally, the ACL in the CoPP policy must match the source IP of the NMS; if the ACL is incorrect or if the CoPP class-default drops all traffic, polling fails.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 CoPP policy's ACL does not include the NMS IP address, so SNMP packets from the NMS are dropped by the class-default.
Why this is correct
CoPP policies typically have a class that matches traffic to be permitted; if the NMS is not matched, its packets fall into class-default, which may be set to drop.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
CoPP only affects routing protocol traffic, not SNMP.
Why it's wrong here
CoPP can filter any control plane traffic, including SNMP.
✗
The SNMP community string ACL is overridden by the CoPP policy.
Why it's wrong here
The community string ACL and CoPP are independent; both must permit the traffic.
✗
The router requires a reload for the CoPP policy to take effect.
Why it's wrong here
CoPP policies are applied immediately.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
SNMP Troubleshooting — This question tests SNMP Troubleshooting — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The CoPP policy's ACL does not include the NMS IP address, so SNMP packets from the NMS are dropped by the class-default. — CoPP applies to control plane traffic. If the CoPP policy is misconfigured, it may drop SNMP packets even from permitted sources. Additionally, the ACL in the CoPP policy must match the source IP of the NMS; if the ACL is incorrect or if the CoPP class-default drops all traffic, polling fails.
What should I do if I get this 300-410 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 300-410 NAT questions on configuration and troubleshooting.
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?
Static NAT maps one inside address to one outside address.
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