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INCIDENT #198 · SECURITY

Backup network: The new service host fails its network check

Hard25 minutesPro lab

The incident

Backup agents traverse a routed storage boundary while replication monitoring and a lab tenant share a separate branch. Four routed leaves share two spines; clients and services use separate access handoffs while partner and monitoring traffic terminate on other leaves. The primary service transport succeeds to .10 but fails to .200 in the same destination subnet. ICMP to both addresses still works. Investigate backup transport from R1: 10.175.160.0/24 to 10.175.174.0/24 (TCP/2049), and 10.175.161.0/24 to 10.175.175.0/24 (UDP/111).

Your objective

Restore both authorized service transports and return reachability, including clients and service hosts in both halves of the primary subnet. Keep R5 blocked from both service transports, keep SSH blocked to both service subnets, and preserve monitoring between R1 and R6. Do not change physical topology or addressing. These are network forwarding checks, not application-level transactions.

The network

Network topology8 devices 10 links

Backup network: The new service host fails its network check — network topologyR1: Client edge. R2: Client leaf. R3: Spine A. R4: Spine B. R5: Partner leaf. R6: Monitoring leaf. R7: Service leaf. R8: Service gateway. R1 connects to R2. R2 connects to R3. R2 connects to R4. R5 connects to R3. R5 connects to R4. R6 connects to R3. R6 connects to R4. R7 connects to R3. R7 connects to R4. R7 connects to R8. Connections show physical links, not service health.R1 ↔ R2 · 10.175.176.0/30R2 ↔ R3 · 10.175.177.0/30R2 ↔ R4 · 10.175.178.0/30R5 ↔ R3 · 10.175.179.0/30R5 ↔ R4 · 10.175.180.0/30R6 ↔ R3 · 10.175.181.0/30R6 ↔ R4 · 10.175.182.0/30R7 ↔ R3 · 10.175.183.0/30R7 ↔ R4 · 10.175.184.0/30R7 ↔ R8 · 10.175.185.0/30R1Client edgeR1 · Client edge · Starting deviceR2Client leafR2 · Client leafR3Spine AR3 · Spine AR4Spine BR4 · Spine BR5Partner leafR5 · Partner leafR6MonitoringleafR6 · Monitoring leafR7Service leafR7 · Service leafR8ServicegatewayR8 · Service gateway
Physical links · Service health not shown
Link addressing (10)
  • R1 R210.175.176.0/30
  • R2 R310.175.177.0/30
  • R2 R410.175.178.0/30
  • R5 R310.175.179.0/30
  • R5 R410.175.180.0/30
  • R6 R310.175.181.0/30
  • R6 R410.175.182.0/30
  • R7 R310.175.183.0/30
  • R7 R410.175.184.0/30
  • R7 R810.175.185.0/30
8 devices · Cisco IOS syntax · Simulated network

What you’ll practice

acl wildcardsdestination matchingtransport testing

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