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INCIDENT #032 · OSPF

An empty neighbor table

Medium20 minutesPro lab

The incident

Milwaukee branch. Each of three routed leaves connects to both spines. Partner monitoring and service gateways sit behind different leaves. 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: 10.205.0.0/24 to 10.205.10.0/24 (TCP/443), and 10.205.1.0/24 to 10.205.11.0/24 (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 R7. Do not change physical topology or addressing. These are network forwarding checks, not application-level transactions.

The network

Network topology7 devices 8 links

An empty neighbor table — network topologyR1: Client leaf. R2: Spine A. R3: Spine B. R4: Partner leaf. R5: Service leaf. R6: Service gateway. R7: Monitoring edge. R1 connects to R2. R1 connects to R3. R4 connects to R2. R4 connects to R3. R5 connects to R2. R5 connects to R3. R5 connects to R6. R4 connects to R7. Connections show physical links, not service health.R1 ↔ R2 · 10.205.16.0/30R1 ↔ R3 · 10.205.17.0/30R4 ↔ R2 · 10.205.18.0/30R4 ↔ R3 · 10.205.19.0/30R5 ↔ R2 · 10.205.20.0/30R5 ↔ R3 · 10.205.21.0/30R5 ↔ R6 · 10.205.22.0/30R4 ↔ R7 · 10.205.23.0/30R1Client leafR1 · Client leaf · Starting deviceR2Spine AR2 · Spine AR3Spine BR3 · Spine BR4Partner leafR4 · Partner leafR5Service leafR5 · Service leafR6ServicegatewayR6 · Service gatewayR7MonitoringedgeR7 · Monitoring edge
Physical links · Service health not shown
Link addressing (8)
  • R1 R210.205.16.0/30
  • R1 R310.205.17.0/30
  • R4 R210.205.18.0/30
  • R4 R310.205.19.0/30
  • R5 R210.205.20.0/30
  • R5 R310.205.21.0/30
  • R5 R610.205.22.0/30
  • R4 R710.205.23.0/30
7 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.