Route table and Route Selection Algorithm

Route table and Route Selection Algorithm standard route table www.2cto.com 1. The next route entry's basic idea route table only specifies the next step from the router to the destination path, without knowing the complete path to the destination. 2. The standard IP route table contains many (N, R) pairs, such as ordinal N: IP address of the destination network R: IP address of the next vro on the N path. Basic next-Stop routing selection algorithm: routedatasync (dataphin, RoutingTable) {extracts the destination IP address D from datax and calculates the netid network number N; if N matches the network address directly connected to the vro. Then is directly delivered to the vro (encapsulation, physical address binding, and sending) elseIf RoutingTable contains the N route Then and sends the datax to the next Else route selection error specified in RoutingTable} Static Routing and dynamic routing Static Routing are created and managed manually, it does not automatically change and must be updated manually to reflect changes in the Internet Topology or connection mode. Static Routing features: it is safe, reliable, simple, and intuitive, avoiding the overhead of dynamic routing. Disadvantage: Not Suitable for complex Internet structures: the establishment and maintenance work is heavy, and routing loops are prone to appear. When a fault occurs on the internet, Static Routing does not automatically change the applicable environment: the dynamic routing of the less complex Internet structure can be automatically modified and refreshed through self-learning. Dynamic Routing requires constant exchange of route information between routers. Dynamic Routing features: Advantages: more autonomy and flexibility disadvantages: Switching route information requires network bandwidth; Dynamic Modification and refresh of Route tables requires the memory and CPU processing time of the router, consume vro resources. Applicable environment: the Internet automatically resolves incorrect paths with complex topology structures and a large network scale. The path measurement value with better performance is automatically selected. metric indicates the path advantages and disadvantages. The smaller the metric, the better the path. Metric computing can be based on one feature of a path or multiple features of a path. Hop count: the number of routers that must pass through when the IP datagram arrives at the destination. Bandwidth: The data capability of the link. Latency: the time required to send data from the source to the destination. Load: Number of active information flows in the network (such as routers or links) Reliability: Error Rate overhead during data transmission: a variable value, generally, the network administrator can specify the bandwidth, construction fee, maintenance fee, and usage fee. Routing Protocol: 1. Use the basic condition vro of dynamic routing to run the same routing protocol and execute the same routing algorithm. 2. Widely used routing protocol routing information protocol RIP: Open Shortest Path Priority Protocol OSPF using vector-Distance Algorithm: Link-State algorithm 3. Concept of Route convergence: all routers on the Internet run the same routing information that is accurate enough to reflect the current Internet topology. Fast convergence is the most desired feature of the routing selection protocol. Routing Algorithm: 1. Vector-distance routing algorithm basic idea: the router periodically broadcasts its own route information to its neighboring routers, it is used to notify neighboring routers of the network they can reach and the distance to the network. The adjacent router can modify and refresh its route table based on the received route information. Advantage: the algorithm is simple and easy to implement. Disadvantages: slow convergence problem: route changes of routers need to be transmitted from neighboring routers like waves. The process is slow and requires a large amount of information to be exchanged: similar to the size of your route table. Applicable environment: Small and Medium Internet with less severe route changes. 2. Basic Idea of the link-State Routing Algorithm: each router on the Internet periodically broadcasts the connection relationship between itself and the adjacent router to other routers. Each router on the Internet uses the received route information to draw an Internet topology. Calculate the shortest path to each network by using the drawn topology and shortest path priority algorithm. Advantages of OSPF route selection Protocol: fast convergence speed; service type selection; load balancing and identity authentication. Disadvantages: High router processing capability and bandwidth requirements. Applicable environment: large-scale and complex environments the principles of the Internet are different: Vector-distance routing selection algorithm: No need for a router to understand the topology of the entire Internet; learn the possible route to each network through the adjacent router. The link-State routing algorithm depends on the topology of the entire Internet. The SPF tree is obtained using the topology of the entire Internet, and then the SPF tree generates the route table.