- A
The NMS is trying to poll a device in VRF BLUE, but the SNMP agent on R7 is not configured to respond to SNMP requests for that VRF because the 'snmp-server vrf' command is missing the 'community' keyword or the VRF is not properly associated with the SNMP process.
The 'snmp-server vrf BLUE community public RO' command is correct, but if the VRF is not defined or the interface is not in the VRF, SNMP may not respond. However, the most common issue is that the NMS's source IP is not in the VRF, so the SNMP agent uses the global routing table to respond, causing a mismatch.
- B
The loopback interface of the device in VRF BLUE is not advertised into the VRF's routing table.
Why wrong: This would cause unreachability, but the NMS would not even get a response. The scenario says the NMS cannot poll, which could be due to routing, but the SNMP configuration is the key.
- C
The SNMP community string 'public' is not allowed in VRF BLUE due to an ACL.
Why wrong: No ACL is mentioned, and the 'snmp-server vrf' command does not include an ACL.
- D
The NMS is using SNMPv3, but the VRF configuration only supports v2c.
Why wrong: The configuration uses v2c community, and the NMS can poll global interfaces, so v3 is not the issue.
Quick Answer
The root cause is that the NMS is trying to poll a device in VRF BLUE, but the SNMP agent on R7 is not configured to respond to SNMP requests for that VRF because the `snmp-server vrf` command is missing the `community` keyword or the VRF is not properly associated with the SNMP process. In MPLS VPN VRF environments, SNMP community strings are global by default, so the `snmp-server vrf BLUE community public RO` command is required to bind the community to the specific VRF; without it, the agent ignores SNMP requests arriving from the VRF’s context, even though the NMS has reachability to the loopback. This scenario tests your understanding of SNMP in MPLS VPN VRF troubleshooting for the Cisco CCNP ENARSI 300-410 exam, where a common trap is assuming that a global `snmp-server community` command covers all VRFs—it does not. Remember the memory tip: “VRF needs its own community command; global is blind to VRF traffic.”
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.
Router R7 is part of an MPLS VPN network. It has multiple VRFs. The NMS is in the global routing table and needs to poll SNMP from devices in VRF BLUE. The configuration includes: snmp-server community public RO, snmp-server vrf BLUE community public RO. However, the NMS cannot poll the loopback interface of a router in VRF BLUE. The NMS can poll R7's global interfaces. What is the root cause?
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 NMS is trying to poll a device in VRF BLUE, but the SNMP agent on R7 is not configured to respond to SNMP requests for that VRF because the 'snmp-server vrf' command is missing the 'community' keyword or the VRF is not properly associated with the SNMP process.
SNMP community strings for VRFs require the 'snmp-server vrf' command to associate the community with the VRF. However, the NMS must have reachability to the VRF's loopback. If the NMS is in the global table, it needs a route to the VRF's loopback via route leaking or MPLS VPN. The issue is that the NMS cannot reach the VRF loopback because there is no route. But the question states the NMS can poll R7's global interfaces, so reachability to R7 is fine. The correct answer is: 'The NMS is trying to poll a device in VRF BLUE, but the SNMP agent on R7 is not configured to respond to SNMP requests for that VRF because the 'snmp-server vrf' command is missing the 'community' keyword or the VRF is not properly associated with the SNMP process.'
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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 trying to poll a device in VRF BLUE, but the SNMP agent on R7 is not configured to respond to SNMP requests for that VRF because the 'snmp-server vrf' command is missing the 'community' keyword or the VRF is not properly associated with the SNMP process.
Why this is correct
The 'snmp-server vrf BLUE community public RO' command is correct, but if the VRF is not defined or the interface is not in the VRF, SNMP may not respond. However, the most common issue is that the NMS's source IP is not in the VRF, so the SNMP agent uses the global routing table to respond, causing a mismatch.
Related concept
Standard ACLs match source addresses.
- ✗
The loopback interface of the device in VRF BLUE is not advertised into the VRF's routing table.
Why it's wrong here
This would cause unreachability, but the NMS would not even get a response. The scenario says the NMS cannot poll, which could be due to routing, but the SNMP configuration is the key.
- ✗
The SNMP community string 'public' is not allowed in VRF BLUE due to an ACL.
- ✗
The NMS is using SNMPv3, but the VRF configuration only supports v2c.
Why it's wrong here
The configuration uses v2c community, and the NMS can poll global interfaces, so v3 is not the issue.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Trap categories for this question
Command / output trap
No ACL is mentioned, and the 'snmp-server vrf' command does not include an ACL.
Scenario analysis trap
This would cause unreachability, but the NMS would not even get a response. The scenario says the NMS cannot poll, which could be due to routing, but the SNMP configuration is the key.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
- Standard ACLs match source addresses.
- Extended ACLs can match source, destination, protocol and ports.
- The first matching ACL entry is used.
- There is usually an implicit deny at the end.
TExam Day Tips
- Check inbound versus outbound direction.
- Read the ACL from top to bottom.
- Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 300-410 ACL questions on filtering logic and placement.
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FAQ
Questions learners often ask
What does this 300-410 question test?
SNMP Troubleshooting — This question tests SNMP Troubleshooting — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The NMS is trying to poll a device in VRF BLUE, but the SNMP agent on R7 is not configured to respond to SNMP requests for that VRF because the 'snmp-server vrf' command is missing the 'community' keyword or the VRF is not properly associated with the SNMP process. — SNMP community strings for VRFs require the 'snmp-server vrf' command to associate the community with the VRF. However, the NMS must have reachability to the VRF's loopback. If the NMS is in the global table, it needs a route to the VRF's loopback via route leaking or MPLS VPN. The issue is that the NMS cannot reach the VRF loopback because there is no route. But the question states the NMS can poll R7's global interfaces, so reachability to R7 is fine. The correct answer is: 'The NMS is trying to poll a device in VRF BLUE, but the SNMP agent on R7 is not configured to respond to SNMP requests for that VRF because the 'snmp-server vrf' command is missing the 'community' keyword or the VRF is not properly associated with the SNMP process.'
What should I do if I get this 300-410 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related 300-410 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Last reviewed: Jun 18, 2026
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