Top OSPF Interview Questions (2024)

1. What is OSPF?

2. How does OSPF elect the Designated Router (DR) and Backup Designated Router (BDR)?

3. What are the advantages of using OSPF?

4. What are OSPF areas?

5. Explain OSPF router types?

6. What is the purpose of OSPF Hello protocol?

7. How does OSPF handle route summarization?

8. What is OSPF authentication, and why is it important?

9. What is OSPF graceful restart?

10. What is OSPF Virtual Link?

11. What is the OSPF metric?

12. How does OSPF prevent routing loops?

13. How can OSPF be optimized for convergence time?

14. Explain OSPF LSA (Link State Advertisement) types?

15. How does OSPF handle equal-cost load balancing?

Q: What is OSPF?
Ans:

The most effective route for IP packet routing in computer networks is determined using OSPF, a dynamic routing protocol. It is based on the link-state database, which is where routers share data about the associated links.

Q: How does OSPF elect the Designated Router (DR) and Backup Designated Router (BDR)?
Ans:

On multiaccess networks like Ethernet, OSPF utilizes the DR and BDR selection processes. The DR is the router with the highest OSPF priority, and the BDR is the router with the second-highest priority. The router with the highest router ID is picked when priorities are equal.

Q: What are the advantages of using OSPF?
Ans:

• Rapid convergence: OSPF updates routing tables in response to network changes quickly.
OSPF supports equal-cost multipath routing, which loads-balances traffic across several paths. Scalability: Large networks with multiple areas can be supported by OSPF. Hierarchical design: Areas are used by OSPF to minimize the effects of changes inside a network.

Q: What are OSPF areas?
Ans:

For scalability and improved resource management, OSPF divides networks into areas. Each area has its own routing table, which minimizes routing updates and reduces the size of the link-state database.

Q: Explain OSPF router types?
Ans:

Various router types are supported by OSPF:

• All interfaces are part of the same OSPF area on the internal router.
• Connects several OSPF areas to the backbone area (Area 0) using a backbone router.
• ABR: A device that connects many places and exchanges routing data.
• Connects OSPF to external networks using the Autonomous System Boundary Router (ASBR).

Q: What is the purpose of OSPF Hello protocol?
Ans:

The OSPF Hello protocol is used to establish and maintain relationships with neighbor. In order to establish adjacency and check the health of nearby routers, OSPF routers exchange Hello packets.

Q: How does OSPF handle route summarization?
Ans:

At ABRs, OSPF performs route summarization. ABRs advertise summarized routes to other areas which reduces the size of routing tables and improve scalability.

Q: What is OSPF authentication, and why is it important?
Ans:

A security part called OSPF authentication confirms the legitimacy of OSPF routing changes. It guarantees that only authorized routers can take part in OSPF and prohibits the entry of malicious routing information into the network.

Q: What is OSPF graceful restart?
Ans:

A router can temporarily restart using the OSPF graceful restart method without losing its OSPF neighbor adjacencies. It supports network stability when routers are reloaded or when software is upgraded.

Q: What is OSPF Virtual Link?
Ans:

To connect two non-backbone areas via the backbone area, OSPF Virtual Link is used. It permits routing between two locations that are not physically connected to one another.

Q: What is the OSPF metric?
Ans:

The OSPF cost or OSPF metric is a cost metric used by OSPF. It is depending on the outgoing interface's bandwidth. The cost is determined using the formula cost = reference bandwidth / interface bandwidth. Usually, the reference bandwidth is set to 100 Mbps.

Q: How does OSPF prevent routing loops?
Ans:

By calculating the shortest path tree using the Dijkstra method and by keeping track of link-state data, OSPF avoids routing loops. To guarantee loop-free routing, OSPF routers exchange routing data and update their link-state databases.

Q: How can OSPF be optimized for convergence time?
Ans:

Optimizing OSPF's convergence time involves:

1. Limiting changes in the network architecture via network design.
2. Powerful hardware and quick network connections to speed up processing.
3. OSPF timers should be properly configured to achieve a balance between convergence speed and stability.
4. Using hierarchical architecture and route summarization to reduce the scope of routing updates.

Q: Explain OSPF LSA (Link State Advertisement) types?
Ans:

The following types of LSAs are used by OSPF to exchange routing data:

1. Type 1: Router LSA: Advertises the status of router's interfaces within an area.
2. Type 2: Network LSA: Advertises the status of a multiaccess network (such as Ethernet).
3. Type 3: Summary LSA: Advertises summarized routes between areas.
4. Type 4: ASBR Summary LSA: Advertises the existence of an ASBR within an area.
5. Type 5: External LSA: Advertises routes into OSPF from outside networks.
NSSA, type 7. Routes from external networks into NSSA areas are advertised by external LSA.

Q: How does OSPF handle equal-cost load balancing?
Ans:

By adding numerous routes with equal costs to the routing table, OSPF offers equal-cost load balancing. The distribution of traffic over various paths boosts the performance and resilience of the network.