Chapters
Narration transcript
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Establish a working baseline
Start with two routers and a working route between their loopbacks.
On this fresh path, the first echo may fail while ARP learns the next hop.
Repeat the ping and check for 100 percent success before saving the baseline.
Save the device configurations, then save a named baseline version.
A baseline gives you evidence to compare with a later fault.
Reproduce one fault
Shut down R2’s uplink to introduce one deliberate fault.
The remote loopback is now unreachable from R1.
Ping R1’s own loopback as a control. That local test still succeeds.
Keep the failed test and the successful control together when diagnosing.
Inspect the evidence
Read the interface status and routing table to locate the broken path.
Open Info to confirm R2’s uplink is administratively down.
Search Events for shutdown and check which device issued the command.
Save a separate fault version, then compare the baseline with the current lab.
The comparison identifies the interface shutdown without a topology change.
Repair and recheck
Use no shutdown on the same interface to repair this fault.
Save the configuration and repeat the original connectivity test.
A successful ping and restored route confirm the path works again.
Compare with the baseline again to verify the saved configuration is restored.