Network Routing Technology and Application (1)

In today's world, network technology is changing with each passing day, and various high-tech network devices, high-bandwidth transmission media, and a variety of network content are emerging, however, all these must be connected, transmitted, distributed, and shared through the network to reflect its high performance and multi-purpose.

1. Introduction to related concepts

1. Concept of routing: routing refers to the activity of transmitting information from the source address to the destination address through an interconnected network. The layer-3 routing occurs in the 0SI network reference model, that is, the network layer.

2. Route Selection: routes require that the information package be sent from one address to another. A route does not specify all routes. It is only a path from the host to the gateway, and then the gateway forwards the packets to the destination host or another gateway.

Route Selection refers to selecting a route for sending packets, and gateway refers to any network device that can complete the routing selection function to connect to different networks.

The routing selection is completed at the IP layer. You do not need to complete the daemon process of routing selection on a host.

The message distance is usually expressed by the number of cross-HOP packets of the gateway, which is called METRIC. The distance from the source address to the destination address of a packet depends on the number of gateways that must pass through the packet. The number of connections between a host and its direct network is zero. If a gateway can be used to reach a specified network, the number of connections between a host and the network is 1.

3. Gateway: the gateway connects two or more networks and provides the routing selection function. The gateway selects a gateway at the network layer. A gateway receives IP data from another gateway, selects a route for it, and sends the IP datagram to another network according to the selected route. The gateway periodically checks the connected network connection status.

The gateway sends packets to the specified destination network according to the specified routes, and the destination network is responsible for sending the packets to the destination host.

4. Route type: A route does not completely describe a complete path. It only defines the path segment from a host to a gateway, or the path segment from a gateway to another gateway.

TCP/IP usually searches the route table in the following order to find the optimal route match:

1) Host Routing: defines the route from the gateway to a specified host;

2) network route: Define a route from the gateway to a specified network segment or network;

3) default route: if neither the host route nor the network route defines a route to the destination, the default route is used.

5. Route table: the route table is defined in the core route table. Each entry in a route table consists of a destination IP address and a gateway address. There are three types of Route tables:

1) direct route entry: when the destination address and the local address are in the same CIDR Block, the direct route entry is used.

2) indirect route entry: when the source and Target Host IP addresses are not in the same CIDR Block, the indirect route entry is used. The destination host is accessed through one or more gateways. The source host only needs to access the first cross-gateway.

3) default route entry: if the target IP address is not in the preceding two route entries, the default route entry is used.
6. Routing Algorithm:

From the above algorithm, we can see that both the host and gateway are involved in the routing selection activity. When an application on the host tries to communicate with another host, the system generates multiple data packets. The IP routing mechanism determines the host or CIDR block to which the datagram is sent based on the network address of the destination IP address.

7. Routing mode: There are three main modes for creating a route: implicit, static, and dynamic.

A route is defined in the core route selection table. Generally, up to 32 routes can be defined. These routing definitions include the local reachable network information, the gateway information connecting to the remote network, and the cross-count that reaches these networks.

Implicit routing is defined and completed when the adapter is configured.

Static Routing is set by the network administrator and requires manual maintenance.

Dynamic Routing is automatically updated by the daemon. Generally, the daemon for routing periodically listens to all routes to refresh the confidence, and broadcasts the received route selection table information so that other routers can update their route selection table.