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INCIDENT #012 · ROUTING

The forgotten subnet

Hard30 minutesPro lab

The incident

Phoenix office. User, partner and service networks meet at one monitored hub. Both service subnets stopped responding after a route cleanup. Monitoring traffic still succeeds and the client route table is not empty. Investigate the two service networks from R1: 10.202.128.0/24 to 10.202.132.0/24 (TCP/443), and 10.202.129.0/24 to 10.202.133.0/24 (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 R2. Do not change physical topology or addressing. These are network forwarding checks, not application-level transactions.

The network

Network topology4 devices 3 links

The forgotten subnet — network topologyR1: User edge. R2: Routed hub. R3: Service gateway. R4: Partner edge. R1 connects to R2. R2 connects to R3. R2 connects to R4. Connections show physical links, not service health.R1 ↔ R2 · 10.202.144.0/30R2 ↔ R3 · 10.202.145.0/30R2 ↔ R4 · 10.202.146.0/30R1User edgeR1 · User edge · Starting deviceR2Routed hubR2 · Routed hubR3ServicegatewayR3 · Service gatewayR4Partner edgeR4 · Partner edge
Physical links · Service health not shown
Link addressing (3)
  • R1 R210.202.144.0/30
  • R2 R310.202.145.0/30
  • R2 R410.202.146.0/30
4 devices · Cisco IOS syntax · Simulated network

What you’ll practice

summary routeslongest prefix matchsafe remediation

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