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INCIDENT #031 · OSPF

Hardening gone sideways

Expert35 minutesPro lab

The incident

Indianapolis campus. Two triangular regional cores meet at a WAN handoff, with the service gateway beyond the remote core. Both service networks are unreachable after a configuration rollout. Restoring the service-edge neighbor alone does not restore every required flow. Investigate the two service networks from R1: 10.204.224.0/24 to 10.204.236.0/24 (TCP/443), and 10.204.225.0/24 to 10.204.237.0/24 (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 R2 blocked from both service transports, keep SSH blocked to both service subnets, and preserve monitoring between R1 and R5. Do not change physical topology or addressing. These are network forwarding checks, not application-level transactions.

The network

Network topology7 devices 8 links

Hardening gone sideways — network topologyR1: Client core. R2: Partner core. R3: West handoff. R4: East handoff. R5: Remote core. R6: Service core. R7: Service gateway. R1 connects to R2. R2 connects to R3. R3 connects to R1. R3 connects to R4. R4 connects to R5. R5 connects to R6. R6 connects to R4. R6 connects to R7. Connections show physical links, not service health.R1 ↔ R2 · 10.204.240.0/30R2 ↔ R3 · 10.204.241.0/30R3 ↔ R1 · 10.204.242.0/30R3 ↔ R4 · 10.204.243.0/30R4 ↔ R5 · 10.204.244.0/30R5 ↔ R6 · 10.204.245.0/30R6 ↔ R4 · 10.204.246.0/30R6 ↔ R7 · 10.204.247.0/30R1Client coreR1 · Client core · Starting deviceR2Partner coreR2 · Partner coreR3West handoffR3 · West handoffR4East handoffR4 · East handoffR5Remote coreR5 · Remote coreR6Service coreR6 · Service coreR7ServicegatewayR7 · Service gateway
Physical links · Service health not shown
Link addressing (8)
  • R1 R210.204.240.0/30
  • R2 R310.204.241.0/30
  • R3 R110.204.242.0/30
  • R3 R410.204.243.0/30
  • R4 R510.204.244.0/30
  • R5 R610.204.245.0/30
  • R6 R410.204.246.0/30
  • R6 R710.204.247.0/30
7 devices · Cisco IOS syntax · Simulated network

What you’ll practice

ospf adjacencyospf advertisementcompound failures

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