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Table of contents
1.
Most Asked OSPF Interview Questions
1.1.
1.What do you understand by OSPF?
1.2.
2. What are the characteristics of OSPF?The main characteristics of OSPF are as follows:
1.3.
3. What are the different types of packets used in OSPF?
1.4.
4. Name different network types in OSPF.
1.5.
5. Name different tables maintained by OSPF.
1.6.
6. Name different OSPF timers.
1.7.
7. What is the default hello and dead interval?
1.8.
8. How does OSPF function or work?
1.9.
9. What are the benefits of dividing the entire network into different areas?
1.10.
10. Explain LSA in OSPF.
1.11.
11. What are the different types of LSA?
1.12.
12. What LSAs are used for inter-area and inter-protocol communication in OSPF?
1.13.
13. Name the multicast IPs used by OSPF?
1.14.
14. Name the parameter that must match for two routers to become neighbors?
1.15.
15. What are different neighbour states in OSPF?
1.16.
16. Name different router types in OSPF?
1.17.
17. What is Backbone Area?
1.18.
18. Is it possible to use OSPF without a backbone area?
1.19.
19. Can two areas exchange or advertise networks if they are not connected to the backbone? If not, what do we need to do to make it happen?
1.20.
20. Explain the concept of Virtual-link in OSPF?
1.21.
21. What do you know about Area Border Router(ABR)?
1.22.
22. Explain Autonomous System Border Router(ASBR)?
1.23.
23. What do you mean by OSPF Router ID?
1.24.
24. What are the DR and BDR in OSPF?
1.25.
25. How DR and BDR are elected in OSPF?
1.26.
26. Does DR/BDR election happen in OSPF Point to Point Network?
1.27.
27. What multicast IPs are used by DR/BDR router?
2.
Conclusion
Last Updated: Jun 12, 2024

Top 27 OSPF Interview Questions and Answers for 2024

Author Aniket Majhi
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Anubhav Sinha
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12 Jun, 2024 @ 01:30 PM

Here's a curated list of the top 27 OSPF(Open Shortest Path First) interview questions and answers, suitable for both freshers and experienced candidates. These questions will aid in interview preparation, boosting confidence, and increasing your chances of securing OSPF related jobs. 

To learn more about Computer Networks related topics, follow this guided path Computer Network.

Top Interview Questions

This article will make you confident before appearing for your upcoming OSPF Interview and will help you extend your knowledge regarding the fundamental concepts of OSPF. So leave all your worries and follow this article till the end to ace your next OSPF Interview Questions.

Now, Without any further ado, let’s start discussing some Top OSPF Interview Questions.

Most Asked OSPF Interview Questions

1.What do you understand by OSPF?

OSPF stands for Open Shortest Path First. It is a standardised link-state routing protocol that utilises Dijkstra's SPF(Shortest Path First) algorithm to calculate the best path and prepares the OSPF database. It is designed to scale efficiently to support larger networks.
 

2. What are the characteristics of OSPF?
The main characteristics of OSPF are as follows:

  • OSPF is a classless routing procedure that supports CIDR and VLSM.
  • It only supports IP routing(both IPv4 and IPv6).
  • The routes have an administrative distance, i.e. 110.
  • It can have unlimited hop count, and it supports limitless hop count.
  • It uses cost as its metric based on the link's bandwidth.
  • It allows the creation of areas and autonomous systems.
     

3. What are the different types of packets used in OSPF?

There are five different types of packers in OSPF:

HELLO

DBD

LSR

LSU

LSack
 

4. Name different network types in OSPF.

The different networks types in OSPF are:

  • Point-to-point network types: This network is used to send data packets between exactly two routers.
  • Broadcast network types: This type of network is used to send data packets from one router to multiple networks in this network type.
  • Non-Broadcast network types: This type of network is used to send data packets to many devices but does not allow broadcasting.
     

5. Name different tables maintained by OSPF.

The different tables maintained by OSPF are as follows:

  • Neighbor table: In OSPF, it stores the neighbor information.
  • Topology table: In OSPF, it stores the topology structure of a network.
  • Routing table: In OSPF, it stores the best routes to all known networks.
     

6. Name different OSPF timers.

There are two types of OSPF times. They are as follows:

  • Hello interval timer: This timer defines how often the OSPF router sends the hello packet to another OSPF router.
  • Dead interval timer: This timer defines how long a router waits for hello packets before it declares the neighbor dead.  
     

7. What is the default hello and dead interval?

By default, the Hello Interval for OSPF is 10 seconds, and the Dead interval in OSPF is four times the Hello interval of 40 seconds.

8. How does OSPF function or work?

OSPF works in the following way:

  • OSPF utilises a hierarchical network design using Areas.
  • It creates neighbor relationships with adjacent routers if the same Area.
  • It advertises the status of directly connected links using Link State Advertisements(LSA).
  • It sends updates(LSAs) when there is a change to one of its links and will only send the change during the update.
  • It uses the Dijkstra Shortest Path First algorithm to calculate the best path and prepares the OSPF database.
     

9. What are the benefits of dividing the entire network into different areas?

The following are the benefits of dividing the whole network into different areas:

  • First, it decreases the routing overhead.
  • It speeds up the convergence.
  • It can confine the network instability to single areas of the network.
     

10. Explain LSA in OSPF.

The LSA stands for Link State Advertisement. It is mainly used in the Link State database to share the basic routing topology information with the other local routers. 
 

11. What are the different types of LSA?

The different types of LSA are as follows:

  • LSA Type 1: Router LSA
  • LSA Type 2: Network LSA
  • LSA Type 3: Summary LSA
  • LSA Type 4: ASBR Summary LSA
  • LSA Type 5: ASBR External LSA
  • LSA Type 6: Multicast OSPF LSA
  • LSA Type 7: Not-so-stubby area(NSSA) External LSA 
  • LSA Type 8: External attribute LSA(OSPFv2) / Link Local LSA(OSPFv3)
  • LSA Type 9: Link Scope Opaque LSA (OSPFv2)/ Intra Arsa Prefix LSA(OSPFv3).
  • LSA Type 10:  Area Scope Opaque LSA
  • LSA Type 11: Autonomous System Scope Opaque LSA

    6.14 OSPF LSA Types – Stuck-in-Active: Journal of an IT-Network  Administrator
                                                                                    
     

12. What LSAs are used for inter-area and inter-protocol communication in OSPF?

For inter-area communication, Type 3 LSA is used.
For inter-protocol communication, Type 4 and 5 are used. 
 

13. Name the multicast IPs used by OSPF?

The multicast IPs used by the OSPF router are 224.0.0.5 and 224.0.0.6.
 

14. Name the parameter that must match for two routers to become neighbors?

The following parameters must be the same for both the routers to become neighbors:

  • Subnet
  • Area id
  • Hello and Dead Interval
  • Authentication
     

15. What are different neighbour states in OSPF?

In OSPF, the neighbour adjacencies will progress through different states, including:

  • Down
  • Init
  • 2-Way
  • ExStart
  • ExChange
  • Loading
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16. Name different router types in OSPF?

The different router types in OSPF are as follows:

  • Internal Router(IR): In OSPF, the internal routers are those whose all interfaces belong to the same area. 
  • Backbone Router(BR): In OSPF, the backbone routers act as internal routers in area 0 (backbone area).
  • Area Border Routers(ABR): In OSPF, area border routers have interfaces belonging to more than one area.
  • Autonomous System Boundary Routers(ASBR): In OSPF, the autonomous system boundary routers are those that advertise external routes into the OSPF domain.
     

17. What is Backbone Area?

In a multi-area OSPF, area 0 is the backbone area. This area is important because all other areas must connect to the backbone area to send their inter-area traffic through the backbone area.
Whether the OSPF ABR Router's loopback network should announce to Backbone  Area? - Network Engineering Stack Exchange
                                                                                         
 

18. Is it possible to use OSPF without a backbone area?

Yes, it is possible to have OSPF without a backbone area. But in that case, only intra-area communication would be possible. But inter-area communication would not be possible without the backbone area.
 

19. Can two areas exchange or advertise networks if they are not connected to the backbone? If not, what do we need to do to make it happen?

No, two areas must be connected to the backbone area to exchange or advertise the network. If it is impossible, we can use the concept of the virtual link.
 

20. Explain the concept of Virtual-link in OSPF?

The virtual link in OSPF is not a physical connection. Rather, it is a logical connection. It uses the cheapest route connecting the ABR of the area that is not connected to the backbone region and the backbone ABR of the transit zone.
OSPF Virtual Link - ME60 V800R010C10SPC500 Feature Description - IP Routing  01 - Huawei
 

21. What do you know about Area Border Router(ABR)?

In OSPF, the Area Border Router(ABR) are router with interfaces belonging to more than one area. It simply connects other areas to the backbone area within an autonomous system.
 

22. Explain Autonomous System Border Router(ASBR)?

In OSPF, the Autonomous System Border Router(ASBR) are those router that advertises external routes into the OSPF domain. It simply connects different autonomous systems.
 

23. What do you mean by OSPF Router ID?

The OSPF Router ID is mainly used to identify the router. Generally, the Router ID is chosen as the highest IP address of the router’s loopback interface. If there is no loopback present, then the highest IP address of the router's physical interfaces is chosen as the Router ID.
 

24. What are the DR and BDR in OSPF?

In OSPF, the DR stands for the Designated Router, and the BDR stands for the Backup Designated Router. Both of these are used to exchange information between different routers. The selection of the DR and BDR depends upon the network. One router is selected as DR, while another one is the BDR.
 

25. How DR and BDR are elected in OSPF?

Generally, the router with the Highest Priority becomes the DR and the router with the second highest priority becomes the BDR. In case of any tie, the router with the highest Router ID will be elected as DR.
Why Does the show ip ospf neighbor Command Reveal Neighbors Stuck in  Two-Way State? - Cisco

This election process is not preemptive. If another router with higher priority is added to the network, it won’t become the DR until we clear the OSPF process. After that, again, the election takes place.
 

26. Does DR/BDR election happen in OSPF Point to Point Network?

No, for a point-to-point network, no election happens. 
 

27. What multicast IPs are used by DR/BDR router?

For DR/BDR it uses 224.0.0.5 and 224.0.0.6. DR/BDR will use the 224.0.0.6 while replying to the Broadcast Multi-access network OSPF routers.

Conclusion

In this article, we have extensively discussed the Top OSPF Interview Questions. We covered some of the important OSPF Interview Questions generally asked in the OSPF interview.

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