Open Shortest Path First Interview Questions

OSPF is link-state routing protocol . It is most widely used Interior Gateway Protocol . It computes the shortest path route using a method based on Dijkstra’s algorithm . It allows routers to dynamically learn routes from one router and advertise that route to other routers . In this article we will discuss about some important Open Shortest Path First interview questions . If you are interviewing related to network administrator , this article is useful for you .

So Let’s start one by one Open Shortest Path First interview questions .

Open Shortest Path First Interview Questions

1. What is OSPF ?

OSPF stands for Open Shortest Path First . It is a link-state routing protocol. It is designed to support large network.

2. What is the Administrative Vlaue (AD) of OSPF ?


3. What are the characteristics of OSPF ?

The main characteristics of OSPF are –

  • It support VLSM and CIDR
  • It support unlimited hop count
  • It support both IPv4 and IPv6
  • It uses cost as its metric , which is computed based on bandwidth of link

4. What is router-id ?

It is a 32 bit unique identifier for each router.

5. What is LSA ?

LSA stands for Link State Advertisement . It hold topology information . It held in memory in the LSDB .

6. What is LSDB ?

LSDB stands for Link State Database . It stores LSA information .Each router has its own LSDB.

7. What is OSPF area ?

It is a logical collection of OSPF network , routers and link . OSPF network is divided into many smaller OSPF area , That’s why reducing the LSDB size .

8. What are the types of LSA in OSPF ?

types of LSA are –

  • Router LSA
  • Network LSA
  • Summary LSA
  • Summary ASBR LSA
  • External LSA
  • Multicast OSPF LSA

9. What are OSPF neighbor states ?

Down – send hello but not receive

Attempt – valid only for manually configuration neighbor

Init – receive hello from neighbor

2way – receive router id

Exstart – master/slave relationship stablished

Exchange – Check LSA in the database .

Loading – Actual exchange of OSPF information

Full – fully synchronized database

10. What is the configuration to change hello and dead interval ?

R# conf t

# in Se 0/0

# ip ospf hello-interval 10

# ip ospf dead-interval 40

11. What is Designated router and Backup Designated router ?

OSPF elect one router as  a Designated router and one router as Backup designated router on the network . DR has highest priority in the network whereas BDR has second highest priority . The router has 0 priority dies not participate in DR/BDR selection .

Every router send LSA to DR through

DR send LSA to all router through

12. How to configure OSPF on your router ?

#conf t

#router ospf 10

#network area 0

#network area 0

13. How to configure router-id on router ?

R#conf t

#router ospf 10

#router id

#clear ip ospf process

14. How to calculate OSPF cost ?

cost = Reference bandwidth/interface bandwidth

Reference bandwidth = 100 mbps

15. Explain tables maintain by OSPF ?

  • Neighbor table – store information about OSPF neighbor
  • Topology table – store topology structure of network
  • Routing table – store best route to all know network

In this article we discuss about Open Shortest Path First interview question . I hope this is useful for you.