Introduction to Dynamic Routing

Introduction to dynamic routing different routing protocols use different measurements. Sometimes multiple measurement hops bandwidth Load Measurement reflects the traffic usage of links along the way. Unlike the number of hops and bandwidth, the load on the path will change, so the measurement will also change. If the measurement changes too frequently, the routing swing (frequent change of the Optimal Path) may occur frequently; the routing swing will negatively affect the bandwidth of the router, the bandwidth of the data link, and the stability of the whole network. www.2cto.com the latency reliability measurement is used to measure the possibility of link failure under certain circumstances; reliability is changed or fixed; the number of link failures or the number of errors received within a specific interval is an example of variable reliability measurement; the fixed reliability measurement is based on the known amount of a link determined by the Administrator. The cost is a general term used to describe the advantages and disadvantages of a route. The minimum cost (maximum cost) or the shortest (longest) only refers to a view of the routing protocol on the path based on its specific measurement. The administrator can manually define the cost to converge dynamic routing. The selection protocol must contain a series of processes, these processes are used to notify other routers of the local direct connection network, Receive and process similar information from other routers, and relay the information received from other routers. In addition, the routing protocol also needs to define the measurement that determines the optimal path. For the routing protocol, another criterion is that the reachable information in the route tables of all routers on the interconnected network must be consistent. The process of making all route tables consistent is called "convergence "; the sum of the time it takes for information sharing across the network and for all routers to calculate the optimal path is the "convergence time" Dynamic Routing Protocol Classification 1 A group of internal and external gateway protocols under the common management domain A set of routers running the same routing selection protocol is an Autonomous System (Autonomous System, AS); in the Internet, an autonomous system is a unit (an enterprise, city, or isp) that has the right to determine which Routing Protocol the system uses. With the development of the network, the above definition of AS is no longer very accurate. The development of the network leads to frequent network convergence between networks, resulting in more and more routing protocols used in the same autonomous system, therefore, the autonomous system should be defined as an interconnected network under the joint management; www.2cto.com Internal Gateway Routing Association (IGP): used for decision-making routing in a single autonomous system; including RIP, OSPF, IS-IS, and other external Gateway Routing Protocols (EGP ): it is used to execute routes between multiple autonomous systems. For example, bgp igp is used to solve AS internal communication, EGP is the origin of the 2-distance vector and link-State Routing Protocol distance vector name for inter-AS communication because the route is a vector (distance, direction) the distance is defined according to the measurement (using 'hops 'as the measurement), and the direction is defined according to the next hop router; for example, the "downward hop in the direction of router X, based on which the distance is 5 hops," indicates that each router learns the route information they observe from the neighboring router, then, we will advertise the route information we observed. Because each router depends on the neighboring router in the information, and the neighboring router learns the route from their neighboring router, therefore, distance vector routing is sometimes referred to as "Routing Based on rumors" www.2cto.com. The information used by distance vector routing protocol can be compared to the information provided by 'road; the link status routing protocol is like a public A router in the link status is not prone to spoofing and making wrong routing decisions, because it has a complete network diagram; the link status is different from the distance vector routing method based on rumors. The reason is that the link status router obtains first-hand information from the peer router. Each router generates some information about itself, information about the local smart connection network and the status of these links. This information is transmitted from one vro to another. Each vro backs up the information, but never changes the information; the ultimate goal is that each vro has the same information about the interconnected network, and each vro can calculate its optimal path independently; to understand the concept of several distance vector routing protocols, regular update means literal update. It should be noted that if the update information is sent too frequently, blocking may occur, however, if the update information is not sent frequently, the network convergence time may be long and cannot be accepted by the neighbor distance vector routing protocol to send the update information to the adjacent router, and the neighbors are dependent on passing update information to their neighbors. Therefore, distance vector routing is said to be broadcast and updated in the "Hop-by-hop update mode" www.2cto.com. How do I find other routers when the vro is activated on the network for the first time? How does it declare its own existence? The simplest method is to send an update message to the broadcast address (255.255.255.255.255 in an IP address). A neighbor router using the same route selection protocol will receive the broadcast packet and take corresponding actions; hosts and other devices that do not care about route update information will discard this packet. The full route table updates most distance vector routing protocols use a very simple way to tell neighbors what they know, this method broadcasts the entire route table. After receiving the update information, the neighbor collects the information required by the host, and the other information is discarded.