Branch WAN: The service edge loses its neighbor
The incident
Branch resolvers reach a central DNS service across a regional aggregation router and a WAN handoff. Independent north and south core paths connect the ingress and egress routers. The directly connected service-edge link responds, but the OSPF adjacency across it is absent. Other adjacencies and monitoring traffic remain healthy. Investigate central DNS transport from R1: 10.164.96.0/24 to 10.164.106.0/24 (TCP/53), and 10.164.97.0/24 to 10.164.107.0/24 (UDP/53).
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
Link addressing (6)
- R1 R2
10.164.112.0/30 - R2 R3
10.164.113.0/30 - R2 R4
10.164.114.0/30 - R3 R5
10.164.115.0/30 - R4 R5
10.164.116.0/30 - R5 R6
10.164.117.0/30
What you’ll practice
Interview exercises are inspired by common industry competencies. They are not proprietary interview questions.