Learn the routing protocol from the principle

Our network is growing. The routing protocol is used to transmit and send information in these networks. How is the guiding rule in the network road formed? Today, let's take a look at the concept of the routing protocol. First, let's take a look at the routing principle.

When one host in the IP subnet sends an IP group to another host in the same IP subnet, it will directly send the IP Group to the network, and the other party will receive it. To send the IP address to a host on the internet, you need to select a router that can reach the destination subnet and send the IP address group to the router. The router is responsible for sending the IP address group to the destination. If such a router is not found, the host sends the IP Group to a router called "default gateway. The "Default Gateway" is a configuration parameter on each host. It is the IP address that is connected to a vro port on the same network.

When forwarding an IP group, the router selects an appropriate port based on the network number of the destination IP address of the IP Group and sends the IP Group out. Like a host, the vro must determine whether the port is connected to the destination subnet. If yes, the group is directly sent to the network through the port. Otherwise, the next vro must be selected to send the group. The router also has its default gateway to send IP groups that do not know where to send them. In this way, the router correctly forwards IP groups that know how to transfer them, and the IP groups that do not know are sent to the "Default Gateway" router. In this way, the IP Group will eventually be sent to the destination, IP groups that cannot be sent to the destination are discarded by the network.

Currently, all TCP/IP networks are interconnected through routers. The Internet is an international network that connects thousands of IP subnets through routers. This type of network is called router-based network ". In "inter-network", routers are not only responsible for forwarding IP groups, but also responsible for communicating with other routers to jointly determine the routing selection and maintenance route table of "inter-network.

The routing action includes two basic items: path finding and forwarding. The routing algorithm is used to determine the optimal path to the destination. Because different routing protocols and routing algorithms are involved, it is relatively complicated. To determine the optimal route, the routing algorithm must start and maintain the route table containing route information. The routing information varies depending on the routing algorithm used. The routing algorithm fills in different information collected in the routing table, and tells the router about the relationship between the destination network and the next stop nexthop according to the route table. The router interconnection information is updated, and the route table is updated and maintained so that the network topology changes are correctly reflected. The optimal path is determined by the router according to the measurement. This is the routing protocol), such as the routing information protocol RIP), Open Shortest Path Priority protocol OSPF) and Border Gateway protocol BGP.

Forward refers to the information transfer group along the best path for path searching. The router first looks up in the routing table and determines whether the router knows how to send the group to the next station router or host). If the router does not know how to send the group, the router usually discards the group; otherwise, the group is sent to the next site based on the corresponding table items in the route table. If the destination network is directly connected to the vro, The vro sends the group directly to the corresponding port. This is the route forwarding protocol (routed protocol ).

The routing forwarding protocol and the routing selection protocol are mutually compatible and independent. The former uses the route table maintained by the latter, and the latter uses the functions provided by the former to publish the Routing Protocol Data grouping. The routing protocols mentioned below, unless otherwise stated, refer to the routing selection protocols, which are also common habits.

Routing Protocol

Typical routing methods include Static Routing and dynamic routing.

Static Routing is a fixed route table set in a vro. The static route does not change unless the network administrator intervene. Because Static Routing cannot reflect network changes, it is generally used in a network with a small network size and a fixed topology. Static Routing is simple, efficient, and reliable. Among all the routes, static routes have the highest priority. When a dynamic route conflicts with a static route, the static route prevails.

Dynamic routing is a process in which routers in the network communicate with each other, transmit route information, and update the router table using the received route information. It can adapt to network structure changes in real time. If the route update information indicates that the network has changed, the route selection software recalculates the route and sends new route update information. This information is transmitted through various networks, causing routers to restart their routing algorithms and update their route tables to dynamically reflect network topology changes. Dynamic Routing is suitable for networks with large networks and complex network topologies. Of course, various dynamic routing protocols occupy network bandwidth and CPU resources to varying degrees.

Static Routing and dynamic routing have their own characteristics and applicability. Therefore, dynamic routing is usually used as a supplement to Static Routing in the network. When a group is used to find the route in the vro, The vro first searches for the static route. If yes, the vro。 forwards the route according to the corresponding static route forwarding group. Otherwise, the vro searches for the dynamic route.