HomeIncident briefing
Back to the library
INCIDENT #007 · ROUTING

The missing way home

Hard25 minutesFree lab

The incident

Austin service network. Independent north and south core paths connect the ingress and egress routers. 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: 10.201.224.0/24 to 10.201.234.0/24 (TCP/443), and 10.201.225.0/24 to 10.201.235.0/24 (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 topology6 devices 6 links

The missing way home — network topologyR1: Client edge. R2: Ingress. R3: North core. R4: South core. R5: Egress. R6: Service gateway. R1 connects to R2. R2 connects to R3. R2 connects to R4. R3 connects to R5. R4 connects to R5. R5 connects to R6. Connections show physical links, not service health.R1 ↔ R2 · 10.201.240.0/30R2 ↔ R3 · 10.201.241.0/30R2 ↔ R4 · 10.201.242.0/30R3 ↔ R5 · 10.201.243.0/30R4 ↔ R5 · 10.201.244.0/30R5 ↔ R6 · 10.201.245.0/30R1Client edgeR1 · Client edge · Starting deviceR2IngressR2 · IngressR3North coreR3 · North coreR4South coreR4 · South coreR5EgressR5 · EgressR6ServicegatewayR6 · Service gateway
Physical links · Service health not shown
Link addressing (6)
  • R1 R210.201.240.0/30
  • R2 R310.201.241.0/30
  • R2 R410.201.242.0/30
  • R3 R510.201.243.0/30
  • R4 R510.201.244.0/30
  • R5 R610.201.245.0/30
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.