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INCIDENT #026 · ROUTING

The one-way change

Hard25 minutesPro lab

The incident

Buffalo service network. Client, partner and service access branches attach to different vertices of a routed core triangle. Requests reach both service networks, but the second client subnet cannot receive replies. The first client subnet still works. Investigate the two service networks from R1: 10.204.64.0/24 to 10.204.74.0/24 (TCP/443), and 10.204.65.0/24 to 10.204.75.0/24 (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

The one-way change — 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 · 10.204.80.0/30R2 ↔ R3 · 10.204.81.0/30R3 ↔ R5 · 10.204.82.0/30R5 ↔ R2 · 10.204.83.0/30R3 ↔ R4 · 10.204.84.0/30R5 ↔ R6 · 10.204.85.0/30R1Client 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 R210.204.80.0/30
  • R2 R310.204.81.0/30
  • R3 R510.204.82.0/30
  • R5 R210.204.83.0/30
  • R3 R410.204.84.0/30
  • R5 R610.204.85.0/30
6 devices · Cisco IOS syntax · Simulated network

What you’ll practice

return pathstatic routingbidirectional verification

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