Also known as shortest path Routing algorithm.

Link states:

Information about the state of (Router interfaces) links is known as link-states. As you can see in the figure, this information includes:

  • The interface's IP address and subnet mask.
  • The type of network, such as Ethernet (broadcast) or Serial point-to-point link.
  • The cost of that link.
  • Any neighbor routers on that link.



So exactly how does a link-state routing protocol work? All routers will complete the following generic link-state routing process to reach a state of convergence:

  1. Each  router learns   about its own   links,   its   own   directly    connected This is done by detecting that an interface is in the up state.
  2. Each router is responsible for meeting its neighbors on directly connected networks. link state routers do this by exchanging Hello packets with other link-state routers on directly connected networks.
  3. Each router builds a Link-State Packet (LSP) containing the state of each directly connected link. This is done by recording all the pertinent information about each neighbor, including neighbor ID, link type, and bandwidth.
  4. Each router floods the LSP to all neighbors, who then store all LSPs received in a Neighbors then flood the LSPs to their neighbors until all routers in the area have received the LSPs. Each router stores a copy of each LSP received from its neighbors in a local database.
  5. Each router uses the database to construct a complete map of the topology and computes the best path to each destination network. Like having a road map, the router now has a complete map of all destinations in the topology and the routes to reach them. The SPF algorithm is used to construct the map of the topology and to determine the best path to each network.

Advantages of Link state Routing protocol

Build the topological map:

Link-state routing protocols create a topological map, or SPF tree of the network topology. Distance vector routing protocols do not have a topological map of the network.

Faster Convergence:

When   receiving   a   Link-state   Packet   (LSP),   link-state    routing    protocols immediately flood the LSP out all interfaces except for the interface from which the LSP was received. This way, it achieves the faster convergence. With distance vector routing algorithm, router needs to process each routing update and update its routing table before flooding them out other interfaces.

Event Driven Updates:

After the initial flooding of LSPs, link-state routing protocols only send out an LSP when there is a change in the topology. The LSP contains only the information regarding the affected   link.   Unlike   some   distance    vector routing protocols, link-state routing protocols do not send periodic updates.