Cisco Certified Support Technician (CCST) NetworkingIP ConnectivityHard
A network engineer is configuring OSPFv3 on a router for an IPv6 network. Two directly connected routers are failing to establish an OSPFv3 adjacency. Upon investigation, they discover that the OSPFv3 hello and dead timers are mismatched between the two routers. What is the consequence of mismatched OSPFv3 timers?
- AIt will cause the OSPFv3 router ID to change dynamically.
- BIt will result in an OSPFv3 adjacency not being formed.
- CIt will only affect LSU (Link-State Update) packet exchange, not adjacency.
- DIt will cause slower OSPFv3 convergence.
Show answer & explanationAnswer & explanation
Correct answer: B. It will result in an OSPFv3 adjacency not being formed.
OSPFv3 (like OSPFv2) requires that certain parameters, including hello and dead timers, match between directly connected neighbors to form and maintain an adjacency. If these timers are mismatched, the routers will not form an adjacency, preventing routing information exchange.
Why the other options are wrong
- A. The OSPFv3 router ID is typically a fixed 32-bit value, not dynamically changed by mismatched timers.
- C. LSU exchange is part of the adjacency process; if adjacency isn't formed, LSUs cannot be exchanged properly.
- D. Slower convergence might be an indirect consequence if adjacencies are flapping, but the primary issue is the complete failure to form the adjacency.
OSPFv3 Adjacency Requirements
For two OSPFv3 routers to form an adjacency, several parameters must match between them, including the area ID, authentication (if used), stub area flag, and especially the hello and dead timers.
- Hello and Dead timers must match.
- Area ID must match.
- Authentication type and key must match (if configured).
- Mismatched parameters prevent adjacency formation.
Memory trick: OSPFv3 neighbors must 'agree' on time and place.