Dynamic Routing Protocol-link status

Dynamic Routing Protocol-link status if the distance vector routing protocol is like a road sign, the link status routing protocol is like a map-it owns the entire network. The link status routing protocol is also called the shortest path first or distributed database protocol. Common include OSPF and IS-I S. ### Share all the information it knows from the vector routing protocol, but only share the information with its neighbors. The link status routing protocol only shares the connection with its direct connection, however, this information is shared to all routers in the routing area. Distance Vector routing is prone to loop and infinite loop packets, so horizontal segmentation, route poisoning, and retention time are used to avoid such events. Link Status routing is easier to avoid such situations. More importantly, the distance vector routing protocol is the release route. If an important link is changed, many routes are released. When the link status routing protocol encounters a link change, only publish link change notifications, rather than spreading all related routes. In a word, the difference between the two is whether they calculate routes independently.
The link status Routing Protocol has the following characteristics: Each router establishes an adjacent relationship with its neighbor. Each router sends a link state advertisement (LSA), and an LSA sends a link from each interface of the router, the status of the link, the metric of the router interface to the link, and all the neighbors that may be connected to the link. Each neighbor who receives the LSA forwards the LSA to their neighbor. Each router stores all the LSAs it receives in its database. If everything is normal, the databases of all routers should be the same. The completed topological database or link state database describes a tree from a vro to each network, and then forms a route table. Www.2cto.com forms a neighbor relationship and is maintained as a hello packet. The Router ID indicates the unique identity of the Router in the network.
Link state flooding: after the connection is established, the router starts to send LSA flood. Each received LSA will be sent directly from other egress to the neighbor, so that the link status routing protocol converges very quickly. In the distance vector routing protocol, you must process the received update and send the update regularly. Therefore, the convergence is slow. In the flood process, sequencing and aging are the two most important processes. Sequence Numbers. the router contains a sequence number in the LSA it sends. When the router receives an LSA containing the same route, it checks the sequence number. If it is greater than the sequence number of the route in its topological database, if the received LSA sequence number is less than or equal to the database sequence number, it is discarded. This prevents infinite loop spread of LSA. Sequence number space, which can be divided into linear sequence number space (IS-IS), circular sequence number and Lollipop-shaped sequence number space (the combination of the first two ).
Aging. When an LSA is generated, the router sets the aging to zero. After the LSA is released, the age is added to each vro. MaxAgeDiff. When the vro receives multiple same LSAs with different aging with the same sequence number, if the aging difference does not exceed MaxAgeDiff, The vro considers these differences to be caused by normal network latency, the original LSA will be retained. If the aging exceeds MaxAgeDiff, the router selects the latest LSA and distributes the LSA. A typical MaxAgeDiff is 15 minutes (OSPF ). Maximum age. The age of LSA continues to increase in the link state database. When it is added to Maximum age, the age of this LSA is set to Maximum age and distributed out, and then deleted from the database. The maximum age of OSPF is 1 hour. Link state refresh time. There must be a mechanism for LSA to be reset before reaching Maximum age, otherwise all LSA will be deleted after all. When the Link state refresh time arrives, the router will distribute a new LSA to all neighbors so that the neighbors can reset Maximum age. OSPF is set to 30 minutes.
Link state database: Link state database, also known as topological database, is used to store LSA. Sequence number and age are mainly used to manage the distribution of LSA. The router ID, the network segment connected to it, and the neighbor are used for shortest path calculation. Www.2cto.com LSA mainly contains two types of information: Router link information and Stub network information. The route link information describes the Router's Neighbor (Router ID, Neighbor ID, cost), where cost is the cost to the Neighbor's link; the end Network information describes the end Network (a Network that is not connected to a neighbor) (Router ID, Network ID, cost) connected to a vro ). The SPF algorithm first calculates the shortest path of each vro and then adds the end network to these vrouters. Cost is based on the cost interface at the router egress.
Area: an Area is an internal network composed of a group of routers. The use Area is mainly based on the following considerations: Compared with the distance vector protocol, the vro requires a larger memory; complex algorithms require more CPU processing time; transmitting LSA requires more bandwidth, especially in unstable networks. Dizzy by the author