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INCIDENT #239 · SECURITY

Remote access: The port is open for the wrong traffic

Medium20 minutesPro lab

The incident

Managed remote clients reach access-service gateways over an enterprise transit chain; unmanaged devices use a separate branch. The partner network branches off near ingress while the service sits three transport hops farther away. The primary service port appears in the access list, but its required transport is blocked. Routing and the secondary service are working. Investigate access gateway transport from R1: 10.180.192.0/24 to 10.180.200.0/24 (TCP/443), and 10.180.193.0/24 to 10.180.201.0/24 (UDP/1194).

Your objective

Restore both authorized service transports and return reachability, including clients and service hosts in both halves of the primary subnet. Keep R6 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 5 links

Remote access: The port is open for the wrong traffic — network topologyR1: Client edge. R2: Ingress hub. R3: WAN transit. R4: Service handoff. R5: Service gateway. R6: Partner edge. R1 connects to R2. R2 connects to R3. R3 connects to R4. R4 connects to R5. R2 connects to R6. Connections show physical links, not service health.R1 ↔ R2 · 10.180.208.0/30R2 ↔ R3 · 10.180.209.0/30R3 ↔ R4 · 10.180.210.0/30R4 ↔ R5 · 10.180.211.0/30R2 ↔ R6 · 10.180.212.0/30R1Client edgeR1 · Client edge · Starting deviceR2Ingress hubR2 · Ingress hubR3WAN transitR3 · WAN transitR4ServicehandoffR4 · Service handoffR5ServicegatewayR5 · Service gatewayR6Partner edgeR6 · Partner edge
Physical links · Service health not shown
6 devices · Cisco IOS syntax · Simulated network

What you’ll practice

tcp vs udpacl protocoltransport testing

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