GATE CSE 2023 | Question: 15

Question

Which of the following statements is/are $\text{INCORRECT}$ about the $\textsf{OSPF (Open Shortest Path First)}$ routing protocol used in the Internet?

• A. $\textsf{OSPF}$ implements Bellman-Ford algorithm to find shortest paths.
• B. $\textsf{OSPF}$ uses Dijkstra's shortest path algorithm to implement least-cost path routing.
• C. $\textsf{OSPF}$ is used as an inter-domain routing protocol.
• D. $\textsf{OSPF}$ implements hierarchical routing.

Comments

The correct answer is Option : A & C

Answer 1

Correct answer : A , C

You need to know certain points about OSPF if you are GATE aspirant

• OSPF is an open standard, not related to any particular vendor.
• OSPF is hierarchical routing protocol, using area 0 (Autonomous System) at the top of the hierarchy.
• OSPF uses Link State Algorithm, and an OSPF network diameter can be much larger than that of RIP.
• OSPF supports Variable Length Subnet Masks (LSM)V, resulting in efficient use of networking resources.
• OSPF uses multicasting within areas.
• After initialization, OSPF only sends updates on routing table sections which have changed, it does not send the entire routing table, which in turn conserves network bandwidth.
• Using areas, OSPF networks can be logically segmented to improve administration, and decrease the size of routing tables. 

Comments

can u share the same kind of notes for RIP?

Answer 2

Answer: A, C

OSPF (Open Shortest path First) is an interior gateway protocol (IGP) for routing Internet Protocol (IP) packets within a single routing domain, such as an autonomous system. It gathers link state information from available routers and constructs a topology map of the network.  It computes the shortest-path-tree for each route using a method based on Dijkstra’s algorithm. Ref-1.

OSPF is hierarchical routing protocol, using area 0 (Autonomous System) at the top of the hierarchy. Ref-2

The question is ask about Incorrect options. A, C are the incorrect.

Answer 3

The other statements are correct for the following reasons:

Statement 2: OSPF uses Dijkstra's algorithm to implement least-cost path routing. This is true because OSPF is a link-state routing protocol that uses Dijkstra's algorithm to calculate the shortest path to each node. Each router using OSPF constructs a map of the connectivity to the network, in the form of a graph, and then uses Dijkstra's algorithm to calculate the shortest path to each node.

Statement 4: OSPF implements hierarchical routing. This is also correct. In OSPF, an Autonomous System (AS) can be divided into areas, which group together networks and routers. Routing information is exchanged within an area, but not across areas, which can reduce the amount of routing traffic and make the routing more scalable. Area 0, or the backbone area, forms the top of the hierarchy and is used to connect other areas. This hierarchical design is a key feature of OSPF, allowing it to scale to support large networks.