The most complete routing basics in history

Many people do not know the basic routing knowledge yet. Here we mainly introduce the composition of routing, including route selection, switching, and routing algorithms. We hope this will help you. A route is a behavior that transmits information from the source to the target through the network. On the road, at least one intermediate node is encountered. Routing is usually compared with bridging. In the eyes of careless people, they seem to do the same thing. The main difference between them is that the bridge occurs at the Layer 2 link layer of the OSI Reference protocol, while the routing occurs at the Layer 3 network layer ). This difference allows the two to use different information in the process of transmitting information, so as to complete their tasks in different ways. The routing topic has long been in the computer field, however, it was not until the middle of 1980s that the business was successful. The main reason for this delay was that the network in 1970s was very simple, and later it was common for large networks.

Basic routing knowledge: Route Composition

A route consists of two basic actions: determining the optimal path and transmitting information through the network. In the routing process, the latter is also called data) exchange. The switching is relatively simple, but the selection path is complicated.

Basic routing knowledge: Route Selection

Metric is the Metering Standard used by routing algorithms to determine the optimal path to the destination, such as the path length. To help route selection, the routing algorithm initializes and maintains the route table containing the path information. The path information varies with the routing algorithm used. The routing algorithm fills the route table according to a lot of information. Destination/Next Hop address: the best way to tell the router to reach this destination is to send the group to the router representing the next hop. When the router receives a group, it checks its target address, try to associate the address with its next hop.

The route table can also contain other information. The route table compares metric to determine the optimal path. These metric vary according to the routing algorithm used. The following describes the common metric. Routers communicate with each other and maintain their route tables by exchanging route information. route update information usually includes all or part of Route tables. By analyzing route update information from other routers, this vro can create a network topology. Another example of information sent between routers is the link status broadcast information, which notifies other router senders of the link status. The link information is used to create a complete topology so that the router can determine the optimal path.

Basic routing knowledge: Exchange

The exchange algorithm is relatively simple. It is the same for most routing protocols. In most cases, a host decides to send data to another host. After obtaining the router address in some ways, the source host sends a packet to the physical MAC address of the router. The Protocol address of the packet is directed to the target host.

After checking the Destination Protocol address of the packet, the router determines whether it knows how to forward the packet. If the router does not know how to forward the packet, it is usually discarded. If the vro knows how to forward the IP address, the physical address of the target is changed to the physical address of the next hop and sent to it. The next hop may be the final target host. If not, it is usually another vro, And it will perform the same steps. When a group flows in the network, its physical address is changing, but its Protocol address remains unchanged. The exchange between the source system and the target system is described above. ISO defines the terms used to describe the process in layers. In this term, a network device that does not have the ability to forward packets IS called the end system ES -- end system), and an intermediary system IS called the intermediate system ). IS further divided into ISintradomain IS) and ISinterdomain IS, which can communicate between domains in the routing domain ). Generally, a routing domain is regarded as a part of the network under unified management and complies with a specific group of management rules, also known as the Autonomous system utonomous system ). In some protocols, the routing domain can be divided into routing intervals, but the intra-Domain Routing Protocol can still be used to exchange data within and between intervals.

Basic routing knowledge: Routing Algorithms

Routing Algorithms can be differentiated based on multiple features. First, the specific target of the algorithm designer affects the operation of the routing protocol. Secondly, there are multiple routing algorithms, each of which has different effects on the network and router resources. Finally, the routing algorithm uses a variety of metric, which affects the calculation of the optimal path. The following sections analyze the features of these routing algorithms. Optimization refers to the ability of the routing algorithm to select the optimal path, which is calculated based on the value and weight of metric. For example, a routing algorithm may use hops and latency, but the delay may have a higher weight. Of course, the routing protocol must strictly define the metric algorithm.

Routing Algorithms can also be designed as simple as possible. In other words, the routing protocol must provide its functions efficiently to minimize the overhead of software and applications. This is especially important when the software that implements routing algorithms must run on computers with limited physical resources. Routing algorithms must be robust, that is, they must still be able to handle abnormal or unforeseen events, such as hardware faults, high loads, and incorrect implementations. Because the routers are located at the network connection points, a major problem occurs when they fail. The best routing algorithms are usually those that have been tested by time and proved to be stable under various network conditions.

In addition, the routing algorithm must be able to be quickly aggregated. Aggregation is the process in which all routers agree on the optimal path. When a network event causes a path to be disconnected or unavailable, the router distributes route update information through the network, promotes the calculation of the optimal path, and finally makes an agreement between all routers. Slow aggregation of routing algorithms may cause routing loops or network interruptions. Routing Algorithms should also be flexible, that is, they should quickly and accurately adapt to various network environments. For example, if a CIDR block is disconnected, many routing algorithms will quickly select the second best path for the path that uses the CIDR block after the problem is identified. The routing algorithm can be designed to adapt to network bandwidth, router queue size, and network latency.