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INCIDENT #006 · NETWORK OPERATIONS

Going in circles

Hard25 minutesFree lab

The incident

Denver branch. Three core routers form a routed triangle between separate client and service edges. Addresses in the lower half of the primary service subnet fail, while .200 responds. The secondary service is unaffected. Investigate the two service networks from R1: 10.201.192.0/24 to 10.201.200.0/24 (TCP/443), and 10.201.193.0/24 to 10.201.201.0/24 (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 R3 blocked from both service transports, keep SSH blocked to both service subnets, and preserve monitoring between R1 and R4. Do not change physical topology or addressing. These are network forwarding checks, not application-level transactions.

The network

Network topology5 devices 5 links

Going in circles — network topologyR1: Client edge. R2: Ingress core. R3: Alternate core. R4: Egress core. R5: Service gateway. R1 connects to R2. R2 connects to R4. R2 connects to R3. R3 connects to R4. R4 connects to R5. Connections show physical links, not service health.R1 ↔ R2 · 10.201.208.0/30R2 ↔ R4 · 10.201.209.0/30R2 ↔ R3 · 10.201.210.0/30R3 ↔ R4 · 10.201.211.0/30R4 ↔ R5 · 10.201.212.0/30R1Client edgeR1 · Client edge · Starting deviceR2Ingress coreR2 · Ingress coreR3Alternate coreR3 · Alternate coreR4Egress coreR4 · Egress coreR5ServicegatewayR5 · Service gateway
Physical links · Service health not shown
Link addressing (5)
  • R1 R210.201.208.0/30
  • R2 R410.201.209.0/30
  • R2 R310.201.210.0/30
  • R3 R410.201.211.0/30
  • R4 R510.201.212.0/30
5 devices · Cisco IOS syntax · Simulated network

What you’ll practice

longest prefix matchsubnet boundariesforwarding loops

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