# Link State Routing Algorithm in Data Structure

Link State Routing Algorithm is a routing algorithm used to find the shortest path between two points on a network. It is a type of interior gateway protocol (IGP) used by routers to determine the best path for forwarding packets.

In Link State Routing Algorithm, each router constructs a map of the network by exchanging information about its directly connected links with other routers. This information includes the state of each link (up or down), the cost of sending packets across each link, and the identification of the neighbouring routers.

Once a router has collected all of this information from its neighbours, it uses a shortest path algorithm, such as Dijkstra's algorithm, to calculate the shortest path to each destination. This calculation takes into account the cost of each link and the state of the network. The result is a routing table that contains the best path to each destination on the network.

The Link State Routing Algorithm has several advantages over other routing algorithms. First, it allows for a more accurate representation of the network, since each router has a complete view of the network topology. Second, it allows for faster convergence when changes occur in the network, since routers only need to exchange information about the changes rather than their entire routing tables. Finally, it is more scalable than other routing algorithms, since the amount of routing information that each router needs to store is proportional to the number of links it has, rather than the size of the entire network.

The most commonly used Link State Routing Algorithm is the Open Shortest Path First (OSPF) protocol. OSPF is widely used in large enterprise networks, as it provides a fast and reliable way to route traffic between different parts of the network. OSPF uses a hierarchical design to manage the complexity of large networks, and it supports multiple paths to the same destination, allowing for load balancing and redundancy.

Here is an example of how Link State Routing Algorithm works:

Link State Routing Algorithm is a type of routing algorithm that uses a network's complete topology to calculate the shortest path between two nodes. Here's an example of how Link State Routing Algorithm works:

Consider a network with 5 nodes (A, B, C, D, and E) connected by links with varying costs:

• Link AB has a cost of 5.
• Link AC has a cost of 1.
• Link BD has a cost of 3.
• Link BE has a cost of 6.
• Link CD has a cost of 2.
• Link DE has a cost of 4.

To implement Link State Routing Algorithm, each node in the network first creates a Link State Packet (LSP) that describes its connections to the other nodes in the network. The LSP contains information such as the node's ID, its neighbours, and the cost of each link.

Once all nodes have created their LSPs, they exchange them with each other to build a complete view of the network topology. This complete view is stored in a database called the Link State Database (LSDB).

Next, each node runs the Dijkstra algorithm on the LSDB to calculate the shortest path to every other node in the network. The Dijkstra algorithm iteratively selects the node with the lowest cost to add to the set of nodes that have been visited, and updates the costs of its neighbours accordingly. It continues until all nodes have been added to the set.

In our example, the shortest path from node A to node E is:

``````A -> C (cost 1)
C -> D (cost 2)
D -> E (cost 4)
So the total cost is 1 + 2 + 4 = 7.
``````

Note that in this example, each node had complete knowledge of the network topology, and was able to calculate the shortest path using the Dijkstra algorithm. In real-world networks, Link State Routing Algorithm is typically used in conjunction with protocols such as OSPF (Open Shortest Path First), which automate the creation and exchange of LSPs between nodes.