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INCIDENT #015 · OSPF

The overnight discard

Hard25 minutesPro lab

The incident

Dallas data center. A partner branch shares the aggregation router but not the service handoff. OSPF neighbors and the service /24 route look healthy, but one host at .10 is unreachable. Another host in the same subnet responds. Investigate the two service networks from R1: 10.202.224.0/24 to 10.202.230.0/24 (TCP/443), and 10.202.225.0/24 to 10.202.231.0/24 (TCP/8443).

Your objective

Restore both authorized service transports and return reachability, including clients and service hosts in both halves of the primary subnet. Keep R5 blocked from both service transports, keep SSH blocked to both service subnets, and preserve monitoring between R1 and R3. Do not change physical topology or addressing. These are network forwarding checks, not application-level transactions.

The network

Network topology5 devices 4 links

The overnight discard — network topologyR1: Branch edge. R2: Aggregation. R3: Service handoff. R4: Service gateway. R5: Partner edge. R1 connects to R2. R2 connects to R3. R3 connects to R4. R2 connects to R5. Connections show physical links, not service health.R1 ↔ R2 · 10.202.240.0/30R2 ↔ R3 · 10.202.241.0/30R3 ↔ R4 · 10.202.242.0/30R2 ↔ R5 · 10.202.243.0/30R1Branch edgeR1 · Branch edge · Starting deviceR2AggregationR2 · AggregationR3ServicehandoffR3 · Service handoffR4ServicegatewayR4 · Service gatewayR5Partner edgeR5 · Partner edge
Physical links · Service health not shown
Link addressing (4)
  • R1 R210.202.240.0/30
  • R2 R310.202.241.0/30
  • R3 R410.202.242.0/30
  • R2 R510.202.243.0/30
5 devices · Cisco IOS syntax · Simulated network

What you’ll practice

ospf routinglongest prefix matchcontrol vs data plane

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