After building the LSP each router flood the LSP to all neighbors in the link-state routing process. This is the fourth in step link-state routing process. The neighbor routers receive the LSP and save it in the database. All routers in the same routing area flood the link-state information to each other. When a router receives the LSP from any of its interfaces, then the receiving router immediately sends that LSP to out to all interfaces except the receiving interface. This process continues from the router to router in the same area until all router receives the LSP. When flooding LSP is completed then the link-state routing protocol calculates the SPF algorithm, thus the link-state routing convergence speed is very high.
The routers do not send LSPs periodically like the hello packet. It is only sent during the initial startup of the routing protocol on the router. After that, the LSPs is needed to flood when there are network changes occur in the topology. It is also needed when there are network breakdown occurs or after the network coming back.
The LSPs also included information, such as sequence numbers and aging information, to help manage the flooding LSP process. Each router uses this information to determine if it has already received the LSP from another router or if the LSP has new and updated information than LSP already contained in the link-state database. This process allows a router to keep only the most current information in its link-state database. If we discuss the topology in the previous lesson building the Link State Packet. The R1 will flood the LSP packet to all it interfaces containing the following data.
- R1; FastEthernet network 192.168.0.0/24; Cost 1
- R1 -> R2; Serial point-to-point network; 192.168.1.0/24; Cost 1
- R1 -> R3; Serial point-to-point network; 192.168.3.0/24; Cost 1