In the Link - State Routing Protocol, the router attempts to construct its own internal map of the network topology. It provides the information about whether the link to reach the router is active or not.
Every router will create something called Link state packets.
In the first round every node creates link state packets with the help of “Hello packets”.
Step 1 − Prepare the link state packet at every router.
Step 2 − Every router flood the link state packets to every offer router
At A −
Link state packet B, C, D
Now A can construct the entire graph using the received link protocol.
Like this, every node is able to construct the graph in its own memory. Every node has an entire graph. So every router can apply the Dijkstra algorithm to find the shortest path.
The advantages of link-state routing protocol are as follows −
Fast Network Convergence: It is the main advantage of the link-state routing protocol. Because of receiving an LSP, link-state routing protocols immediately flood the LSP out of all interfaces without any changes except for the interface from which the LSP was received.
Topological Map: Link-state routing uses a topological map or SPF tree for creating the network topology. Using the SPF tree, each router can separately determine the shortest path to every network.
Hierarchical Design: Link-state routing protocols use multiple areas and create a hierarchical design to network areas. The multiple areas allow better route summarization.
Event-driven Updates: After initial flooding of LSPs, the LSPs are sent only when there is a change in the topology and contain only the information regarding that change. The LSP contains only the information about the affected link. The link-state never sends periodic updates.
The disadvantages of link-state routing protocol are as follows −
Memory Requirements − The link-state routing protocol creates and maintains a database and SPF tree. The database and SPF tree required more memory than a distance vector protocol.
Processing Requirements − Link-state routing protocols also require more CPU processing because the SPF algorithm requires more CPU time than distance-vector algorithms just like Bellman-Ford because link-state protocols build a complete map of the topology.
Bandwidth Requirements − The link-state routing protocol floods link-state packet during initial start-up and also at the event like network breakdown, and network topology changes, which affect the available bandwidth on a network. If the network is not stable it also creates issues on the bandwidth of the network.