300-420 Question 114
Select 3A financial institution is implementing a new network design to ensure high availability and fast convergence during link failures. The network is using OSPF as the routing protocol and consists of multiple areas with redundant links. Which of the following design considerations will help achieve optimal convergence in the event of a network failure?
- A
Enable OSPF Fast Hellos to reduce the detection time for failed neighbors.
- B
Configure OSPF LSA throttling to limit the frequency of LSA updates during convergence.
- C
Deploy Bidirectional Forwarding Detection (BFD) for faster failure detection.
- D
Ensure all areas are designed as OSPF Stub Areas to minimize LSA flooding.
- E
Tune OSPF timers by reducing the Dead Interval and Hello Interval values.
Show answer and explanation
Correct answers: A, C, E
Explanation
Fast convergence in OSPF can be achieved by reducing failure detection times and optimizing routing protocol behavior. Using OSPF Fast Hellos and reducing OSPF timer intervals (Hello and Dead Intervals) minimizes the time required to detect a failed neighbor. Additionally, deploying BFD provides faster failure detection than OSPF's native mechanisms. However, OSPF Stub Areas and LSA throttling do not directly contribute to faster convergence and may be more applicable for scalability and limiting resource usage rather than failure recovery.
- A. Correct.
Enabling OSPF Fast Hellos reduces the detection time for failed neighbors, which helps in faster convergence. This is a valid design choice.
- B. Incorrect.
Configuring OSPF LSA throttling slows down the frequency of LSA updates, which can delay convergence. This is not ideal for fast convergence.
- C. Correct.
Deploying BFD provides sub-second failure detection, which significantly enhances convergence times. This is a valid design choice.
- D. Incorrect.
Designing all areas as OSPF Stub Areas may reduce LSA flooding but can limit the routing flexibility and scalability. This does not directly contribute to faster convergence in all scenarios.
- E. Correct.
Tuning OSPF timers, such as the Dead Interval and Hello Interval, can help reduce the time taken to detect failed neighbors and support faster convergence. This is a valid design choice.