Important OSPF Interview Questions and Answers

Last Updated: Sep 30, 2013

Jan 15 • Resources • 65260 Views • 47 Comments on Important OSPF Interview Questions and Answers

Open Shortest Path First is abbreviated as OSPF,which is a router protocol. OPSF is used for major autonomous system networks which are in preference to the Routing Information Protocol. OSPF is designated by the Internet Engineering Task Force (IETF) as one of several Interior Gateway Protocols (IGPs). OPSF uses link state routing algo. To fall into the protocol groups made for interior routing to operate into a single autonomous system. Using OSPF systems , a change to a routing table can immediately be masticated to store the information from the other host in the network. This will lead to share same routing information table. Now, understand the Concept of OPSF in terms of questions and answer-

OPSF Interview Questions

QUES 1 What OSPF stands for?
Ans – OSPF is a standardized Link-State routing protocol, designed to scale efficiently to support larger networks.

QUES 2 Mention some characteristics of OSPF
Ans-1) OSPF supports only IP routing.
2) OSPF routes have an administrative distance i.e. 110.
3) OSPF uses cost as its metric, which is computed based on the bandwidth of the link. OSPF has no hop-count limit.

QUES 3 What are different neighbour states in OSPF ?
Ans- Neighbor adjacencies will progress through several states, including:

1)Down
2)Init
3)2-Way
4)ExStart
5)Exchange
6)Loading
7)Advertisements
8)Full

QUES 4 What is role of topology and routing table in OSPF ?
Ans- The OSPF process builds and maintains three separate tables:
1) A neighbor table – contains a list of all neighboring routers.
2) A topology table – contains a list of all possible routes to all known networks within an area.
3) A routing table – contains the best route for each known network.

QUES 5 What different activities neighbour router perform in OSPF?
Ans- A neighbor table includes the following information:
1) The Router ID of each neighbouring router
2) The current “state” of each neighbouring router
3) The interface directly connected to each neighbour
4) The IP address of the remote interface of each neighbour

QUES 6 On which algorithms OSPF depends? What is the principle behind it?
Ans- OSPF uses the Dijkstra Shortest Path First algorithm to determine the shortest path and Link-State Advertisements (LSAs).

Ques 7 Name few types of LSA ?
Ans-
1) Router LSA
2) Network LSA
3) Network Summary LSA
4) ASBR Summary LSA
5) External LSA

QUES 8 Briefly explain functioning and working of different OSPF ?
Ans- Following are working and functioning of OSPF
1) OSPF employs a hierarchical network design using Areas.
2) OSPF forms neighbor relationships with adjacent routers in the same Area.
3) Instead of advertising the distance to connected networks, OSPF advertises the status of directly connected links using Link-State Advertisements (LSAs).
4) OSPF sends updates (LSAs) when there is a change to one of its links, and will only send the change during the updation. LSAs are additionally refreshed every 30 minutes.
5) OSPF uses the Dijkstra Shortest Path First algorithm to determine the shortest path.
6) OSPF is a classless protocol, and thus supports VLSMs.

Ques 9 What are the different OSPF network types and give an example for each ?
Ans- Different OSPF network types with their examples are given below:
1) Broadcast Multi-Access – indicates a topology where broadcast occurs.
Examples include Ethernet, Token Ring, and ATM.

2) Point-to-Point – indicates a topology where two routers are directly connected.
An example would be a point-to-point T1.

3) Point-to-Multipoint – indicates a topology where one interface can connect to multiple destinations. Each connection between a source and destination is treated as a point-to-point link.
An example would be Point-to-Multipoint Frame Relay.

4) Non-broadcast Multi-access Network (NBMA) – indicates a topology where one interface can connect to multiple destinations; however, broadcasts cannot be sent across a NBMA network.
An example would be Frame Relay.

Ques 10 Name tables which OSPF maintain ?
Ans – The OSPF process builds and maintains three separate tables:
1) A neighbor table – contains a list of all neighboring routers.
2) A topology table – contains a list of all possible routes to all known networks within an area.
3) A routing table – contains the best route for each known network.

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