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INCIDENT #063 · OSPF

One connected subnet never entered OSPF

Hard25 minutesPro lab

The incident

The application edge has both service subnets connected. Only 10.143.31.0/24 is absent from the rest of the network; neighbors and the primary application are healthy.

Your objective

Restore the documented flows for 10.143.31.0/24, including the return path to the affected client. Preserve the other service branch, all transit links, and SSH isolation. Do not change interface addresses or the physical topology.

The network

Network topology4 devices 3 links

One connected subnet never entered OSPF — network topologyR1: Client edge. R2: Transit core. R3: Application edge. R4: Telemetry edge. R1 connects to R2. R2 connects to R3. R2 connects to R4. Connections show physical links, not service health.R1 ↔ R2 · 10.143.12.0/30R2 ↔ R3 · 10.143.23.0/30R2 ↔ R4 · 10.143.24.0/30R1Client edgeR1 · Client edge · Starting deviceR2Transit coreR2 · Transit coreR3ApplicationedgeR3 · Application edgeR4Telemetry edgeR4 · Telemetry edge
Physical links · Service health not shown
Link addressing (3)
  • R1 R210.143.12.0/30
  • R2 R310.143.23.0/30
  • R2 R410.143.24.0/30
4 devices · Cisco IOS syntax · Simulated network

What you’ll practice

ospf advertisementcontrol vs data plane

Interview exercises are inspired by common industry competencies. They are not proprietary interview questions.