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INCIDENT #008 · OSPF

A little too quiet

Medium20 minutesFree lab

The incident

Atlanta campus. Client, partner and service access branches attach to different vertices of a routed core triangle. Service reachability disappeared after an OSPF hardening change. Interface addressing is unchanged and the service uplink still responds locally. Investigate the two service networks from R1: 10.202.0.0/24 to 10.202.10.0/24 (TCP/443), and 10.202.1.0/24 to 10.202.11.0/24 (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 R4 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 topology6 devices 6 links

A little too quiet — network topologyR1: Client edge. R2: Client core. R3: Partner core. R4: Partner edge. R5: Service core. R6: Service gateway. R1 connects to R2. R2 connects to R3. R3 connects to R5. R5 connects to R2. R3 connects to R4. R5 connects to R6. Connections show physical links, not service health.R1 ↔ R2 · 10.202.16.0/30R2 ↔ R3 · 10.202.17.0/30R3 ↔ R5 · 10.202.18.0/30R5 ↔ R2 · 10.202.19.0/30R3 ↔ R4 · 10.202.20.0/30R5 ↔ R6 · 10.202.21.0/30R1Client edgeR1 · Client edge · Starting deviceR2Client coreR2 · Client coreR3Partner coreR3 · Partner coreR4Partner edgeR4 · Partner edgeR5Service coreR5 · Service coreR6ServicegatewayR6 · Service gateway
Physical links · Service health not shown
Link addressing (6)
  • R1 R210.202.16.0/30
  • R2 R310.202.17.0/30
  • R3 R510.202.18.0/30
  • R5 R210.202.19.0/30
  • R3 R410.202.20.0/30
  • R5 R610.202.21.0/30
6 devices · Cisco IOS syntax · Simulated network

What you’ll practice

ospf passive interfaceadjacencychange validation

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