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INCIDENT #145 · ROUTING

Regional operations: The second client subnet gets no reply

Hard25 minutesPro lab

The incident

Operations collectors reach polling and trap-receiver networks over three routed transport stages. Parallel three-site metro paths have cross-links at each stage, between independent client and service handoffs. Requests reach both service networks, but the second client subnet cannot receive replies. The first client subnet still works. Investigate monitoring transport from R1: 10.169.0.0/24 to 10.169.14.0/24 (UDP/161), and 10.169.1.0/24 to 10.169.15.0/24 (UDP/162).

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 R5. Do not change physical topology or addressing. These are network forwarding checks, not application-level transactions.

The network

Network topology8 devices 9 links

Regional operations: The second client subnet gets no reply — network topologyR1: Client edge. R2: West north. R3: Central north. R4: East north. R5: West south. R6: Central south. R7: East south. R8: Service gateway. R1 connects to R2. R2 connects to R3. R3 connects to R4. R5 connects to R6. R6 connects to R7. R2 connects to R5. R3 connects to R6. R4 connects to R7. R7 connects to R8. Connections show physical links, not service health.R1 ↔ R2 · 10.169.16.0/30R2 ↔ R3 · 10.169.17.0/30R3 ↔ R4 · 10.169.18.0/30R5 ↔ R6 · 10.169.19.0/30R6 ↔ R7 · 10.169.20.0/30R2 ↔ R5 · 10.169.21.0/30R3 ↔ R6 · 10.169.22.0/30R4 ↔ R7 · 10.169.23.0/30R7 ↔ R8 · 10.169.24.0/30R1Client edgeR1 · Client edge · Starting deviceR2West northR2 · West northR3Central northR3 · Central northR4East northR4 · East northR5West southR5 · West southR6Central southR6 · Central southR7East southR7 · East southR8ServicegatewayR8 · Service gateway
Physical links · Service health not shown
Link addressing (9)
  • R1 R210.169.16.0/30
  • R2 R310.169.17.0/30
  • R3 R410.169.18.0/30
  • R5 R610.169.19.0/30
  • R6 R710.169.20.0/30
  • R2 R510.169.21.0/30
  • R3 R610.169.22.0/30
  • R4 R710.169.23.0/30
  • R7 R810.169.24.0/30
8 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.