Summary
Link-state routing protocols are also known as shortest path first protocols and are built around Edsger Dijkstra's shortest path first (SPF) algorithm. There are two link-state routing protocols for IP: OSPF (Open Shortest Path First) and IS-IS (Intermediate-System-to-Intermediate-System).
The link-state process can be summarized as follows:
1. Each router learns about its own directly connected networks.
2. Each router is responsible for "saying hello" to its neighbors on directly connected networks.
3. Each router builds a Link-State Packet (LSP) containing the state of each directly connected link.
4. Each router floods the LSP to all neighbors, who then store all LSPs received in a database.
5. Each router uses the database to construct a complete map of the topology and computes the best path to each destination network.
A link is an interface on the router. A link-state is the information about that interface including its IP address and subnet mask, the type of network, the cost associated with the link, and any neighbor routers on that link.
Each router determines its own link-states and floods the information to all other routers in the area. As a result, each router builds a link-state database (LSDB) containing the link-state information from all other routers. Each router will have identical LSDBs. Using the information in the LSDB, each router will run the SPF algorithm. The SPF algorithm will create an SPF tree, with the router at the root of the tree. As each link is connected to other links, the SPF tree is created. Once the SPF tree is completed, the router can determine on its own the best path to each network in the tree. This best path information is then stored in the router's routing table.
Link-state routing protocols build a local topology map of the network that allows each router to determine the best path to a given network. A new LSP is sent only when there is a change in the topology. When a link is added, removed or modified, the router will flood the new LSP to all other routers. When a router receives the new LSP, it will update is LSDB, rerun the SPF algorithm, create a new SPF tree, and update its routing table.
Link-state routing protocols tend to have a faster convergence time than distance vector routing protocols. A notable exception is EIGRP. However, link-state routing protocols do require more memory and processing requirements. This is usually not an issue with today's newer routers.
In the next and final chapter of this course, you will learn about the link-state routing protocol, OSPF.
Link-state routing protocols are also known as shortest path first protocols and are built around Edsger Dijkstra's shortest path first (SPF) algorithm. There are two link-state routing protocols for IP: OSPF (Open Shortest Path First) and IS-IS (Intermediate-System-to-Intermediate-System).
The link-state process can be summarized as follows:
1. Each router learns about its own directly connected networks.
2. Each router is responsible for "saying hello" to its neighbors on directly connected networks.
3. Each router builds a Link-State Packet (LSP) containing the state of each directly connected link.
4. Each router floods the LSP to all neighbors, who then store all LSPs received in a database.
5. Each router uses the database to construct a complete map of the topology and computes the best path to each destination network.
A link is an interface on the router. A link-state is the information about that interface including its IP address and subnet mask, the type of network, the cost associated with the link, and any neighbor routers on that link.
Each router determines its own link-states and floods the information to all other routers in the area. As a result, each router builds a link-state database (LSDB) containing the link-state information from all other routers. Each router will have identical LSDBs. Using the information in the LSDB, each router will run the SPF algorithm. The SPF algorithm will create an SPF tree, with the router at the root of the tree. As each link is connected to other links, the SPF tree is created. Once the SPF tree is completed, the router can determine on its own the best path to each network in the tree. This best path information is then stored in the router's routing table.
Link-state routing protocols build a local topology map of the network that allows each router to determine the best path to a given network. A new LSP is sent only when there is a change in the topology. When a link is added, removed or modified, the router will flood the new LSP to all other routers. When a router receives the new LSP, it will update is LSDB, rerun the SPF algorithm, create a new SPF tree, and update its routing table.
Link-state routing protocols tend to have a faster convergence time than distance vector routing protocols. A notable exception is EIGRP. However, link-state routing protocols do require more memory and processing requirements. This is usually not an issue with today's newer routers.
In the next and final chapter of this course, you will learn about the link-state routing protocol, OSPF.
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