Branch WAN: The advertised prefix does not match the service
The incident
Branch resolvers reach a central DNS service across a regional aggregation router and a WAN handoff. Five metro routers provide two directions around the region before the service handoff. The primary service subnet is missing remotely even though a similar-looking network statement exists on the service edge. The secondary subnet works. Investigate central DNS transport from R1: 10.165.32.0/24 to 10.165.42.0/24 (TCP/53), and 10.165.33.0/24 to 10.165.43.0/24 (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 R2 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
10.165.48.0/30 - R2 R3
10.165.49.0/30 - R3 R5
10.165.50.0/30 - R5 R4
10.165.51.0/30 - R4 R1
10.165.52.0/30 - R5 R6
10.165.53.0/30
What you’ll practice
Interview exercises are inspired by common industry competencies. They are not proprietary interview questions.