Lec-40 Link State Routing Algorithm Explained | Computer Network

Summary

In this video, the concept of Link State Routing is explained in-depth using an example network with six routers (A, B, C, D, E, F). The presenter outlines how each router creates its own Link State Table, shares this information through flooding, and then uses Dijkstra’s algorithm to calculate the shortest path to all other routers. The process of constructing routing tables based on these shortest paths is also covered, highlighting how each router figures out the best routes to various destinations. This video provides a comprehensive guide on Link State Routing, ideal for students of network engineering.

Takeaways

• 😀 Link-State Routing is an advanced dynamic routing method compared to Distance Vector Routing.
• 😀 Each router maintains a complete map of the network, including all routers and link costs.
• 😀 Routers detect their neighbors and initially create individual link-state tables.
• 😀 Each link-state table contains neighbors and the distance (cost) to each neighbor.
• 😀 Link-state information is shared across the network using flooding, ensuring all routers have a full network view.
• 😀 Dijkstra's Algorithm is used by routers to calculate the shortest paths to all other routers.
• 😀 Distances to directly connected routers are known, while others are initialized to infinity until calculated.
• 😀 Routers update shortest paths iteratively by comparing current distances with paths through other routers.
• 😀 After computing shortest paths, each router generates its routing table, listing destinations, distances, and next hops.
• 😀 The process ensures efficient routing, accurate network mapping, and dynamic adaptability to network changes.
• 😀 The method is illustrated with a practical example using six routers (A-F) and their link costs, demonstrating step-by-step routing table creation.

Q & A

What is the main difference between Distance Vector Routing and Link-State Routing?

Distance Vector Routing only allows a router to know about its immediate neighbors and their costs, while Link-State Routing enables each router to have a complete map of the network and calculate the shortest path to every other router independently.

What is a Link-State Table and what information does it contain?

A Link-State Table is a table maintained by each router that lists its neighbors and the cost of the connection to each neighbor. It may also include additional information like sequence numbers and TTL (Time To Live).

How do routers share their link-state information in the network?

Routers share their link-state information through a process called flooding, where each router broadcasts its link-state table to all other routers in the network to ensure every router has complete network knowledge.

What is the purpose of using Dijkstra’s algorithm in Link-State Routing?

Dijkstra’s algorithm is used to calculate the shortest path from the source router to all other routers in the network using the complete network map obtained from the link-state tables.

In the example network, what are the neighbors and link costs of Router A?

Router A has neighbors B and C. The cost of the link from A to B is 6, and from A to C is 3.

What does the 'Via' column represent in a routing table?

The 'Via' column indicates the next hop router through which packets should be forwarded to reach the destination router along the shortest path.

Why do routers initially set the distance to non-neighboring routers as infinity?

Non-neighboring routers are initially unknown, so their distances are set to infinity. The actual shortest distances are determined later using Dijkstra’s algorithm as the network topology is discovered.

How does a router determine which path to choose when multiple paths are available?

A router compares the total cost of each available path and selects the path with the minimum cumulative cost to the destination.

What is the first step in Link-State Routing after identifying neighbors?

The first step is to create the individual Link-State Table for each router, listing all directly connected neighbors and the costs to reach them.

What are the advantages of Link-State Routing compared to Distance Vector Routing?

Link-State Routing converges faster, avoids routing loops, and provides a more accurate and complete view of the network, making routing decisions more reliable.

Can the Link-State Routing process be applied to any router in the network?

Yes, the process of creating a link-state table, flooding information, and calculating shortest paths using Dijkstra’s algorithm can be applied independently to any router in the network.