HomeIncident briefing
Back to the library
INCIDENT #177 · SECURITY

Service edge: New client addresses cannot use the service

Medium25 minutesPro lab

The incident

Internal API clients and an independent observability edge share a transit network with an isolated partner segment. The core has two routed branches and a cross-link before the common service handoff. A client at .10 can use the primary service, but a client at .200 in the same subnet cannot. Both clients can reach the monitoring destination. Investigate internal API transport from R1: 10.173.0.0/24 to 10.173.8.0/24 (TCP/8443), and 10.173.1.0/24 to 10.173.9.0/24 (TCP/443).

Your objective

Restore both authorized service transports and return reachability, including clients and service hosts in both halves of the primary subnet. Keep R2 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 topology5 devices 6 links

Service edge: New client addresses cannot use the service — network topologyR1: Client core. R2: North transit. R3: South transit. R4: Egress core. R5: Service gateway. R1 connects to R2. R1 connects to R3. R2 connects to R4. R3 connects to R4. R2 connects to R3. R4 connects to R5. Connections show physical links, not service health.R1 ↔ R2 · 10.173.16.0/30R1 ↔ R3 · 10.173.17.0/30R2 ↔ R4 · 10.173.18.0/30R3 ↔ R4 · 10.173.19.0/30R2 ↔ R3 · 10.173.20.0/30R4 ↔ R5 · 10.173.21.0/30R1Client coreR1 · Client core · Starting deviceR2North transitR2 · North transitR3South transitR3 · South transitR4Egress coreR4 · Egress coreR5ServicegatewayR5 · Service gateway
Physical links · Service health not shown
5 devices · Cisco IOS syntax · Simulated network

What you’ll practice

acl wildcardssource matchingsubnet boundaries

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