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CCNA · 200-301Intermediate

SNMP: Community ACL Blocks the NMS

SNMP polls time out with no error anywhere on the router. Diagnose the community's ACL and fix it yourself, live, right below.

Interactive simNetwork ManagementSNMPACL

Symptom

The community is configured, but the NMS times out. Follow its source ACL and correct the permitted management subnet.

Your mission

Prove the cause, then fix it

Format

Guided CLI investigation

Start interactive labSee the investigation plan ↓Need a hint? Reveal the root cause ↓
SNMP: Community Restricted by the Wrong ACL

Investigate before you configure.

Use the CLI evidence to isolate the fault, make the smallest safe correction, then verify the network state changed.

Observe the symptom and link state.

Diagnose by comparing the protocol evidence.

Verify the expected device state and confirm the original symptom is resolved.

Console access: R1

This workspace stacks for portrait phones. Rotate to landscape for the full split-screen console.

Need a hint?

Reveal the root cause when you're ready.

Try the investigation first, then use this as your escape hatch, not a dead end.

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Lab debrief

Turn the session into a repeatable troubleshooting pattern.

Use this reference after your attempt: first explain the symptom, then verify the evidence, then confirm the repair.

The problem

The NMS at 10.0.50.25 cannot poll R1 with the LabF3bric read-only community. The community exists and the router reports no agent failure, but requests time out.

What you'll practice

  • Explain how SNMP supports network monitoring
  • Read community properties and their attached access list
  • Inspect standard ACL wildcard matching
  • Correct an SNMP source restriction without changing the community
  • Verify that the NMS subnet is admitted

The topology

One network-management station in 10.0.50.0/24 polls a router whose read-only SNMP community is restricted by standard ACL 55.

Commands to run yourself

The real diagnostic commands for this lab, copy-paste ready. Run these in the same order to reproduce the investigation on your own session.

Inspect communities
show snmp community
Inspect source restrictions
show access-lists
Inspect the agent
show snmp

Topology diagram

Frequently asked

Why not change the community string?

The string is valid. The community points to ACL 55, and that ACL permits a different subnet. Rotating the string would leave the same source restriction in place.

Is this ACL applied to an interface?

No. SNMP references it directly as a management-plane source filter, so show ip interface would not reveal this attachment.

Ready to run this lab yourself?

No setup, no image sourcing. Book a session or ask for a live demo.

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