How to grow as a network engineer

In network maintenance, it is indispensable to troubleshoot various network faults. This is a test stone for testing the skill level of a network engineer. There are many people who have a lot of engineering experience, but they basically copy other solutions and type the command code, without really understanding why they are so matched, let alone thinking about whether there is a better implementation solution. When such people encounter a network failure, their eyesight goes black and they have no idea what to do. The fundamental reason is that they do not understand the principles of computer network communication, the technical principles of various functions, and the general configuration ideas of specific functions.

When encountering a network failure, you must first classify the network failure that occurs, whether it is a communication failure, a function implementation failure, or a security issue.

It is easier to analyze communication failures. The key is the peer-to-peer communication principle of the computer network, that is, a message originating from a certain layer at the source must eventually be sent to the corresponding layer at the destination before the message can be processed. for processing. This involves the encapsulation and decapsulation of protocol headers. In addition to the physical layer, during the top-down transmission process of a message originating from a certain layer at the source end, all other layers passing through will encapsulate the protocol header of the protocol running on the corresponding layer. After arriving at the destination end, the packet will be In the bottom-up transmission of a message, the protocol header information of the corresponding layer will be identified each time it reaches a layer, and then the header of that layer will be removed and uploaded to the upper layer until it reaches the corresponding layer of the message originated from the source, and the protocol header information of the corresponding layer will be identified. The protocol header information of this layer is used to process the message. Intermediate network devices (such as switches and routers) usually only understand Layer 2 and Layer 3 protocol header information.

Layer 2 communication mainly involves the issue of VLAN tags. This requires a full understanding of the frame sending and receiving rules of three types of Layer 2 switching ports (Access, Trunk and Hybrid, Cisco equipment only has the first two). Through Analyze the addition or removal of VLAN tags in frames on each link in the communication path to verify whether the frame can accurately reach the other host. For GVRP and MVRP protocols that automatically perform VLAN registration and deregistration, you must have a deep understanding that they can only be enabled on Trunk type ports, and you must have a deep understanding of their VLAN registration and deregistration principles (the two are not exactly the same). In short, in a VLAN environment, communication between users in the same VLAN must abide by a basic rule, that is, each device on the communication path must have registration information for the corresponding VLAN, including the use of dynamic VLAN registration protocols such as GVRP and MVRP.

For three-layer communication, it is much more complicated than two-layer communication because it involves routing issues. But from the perspective of network communication, it is not difficult to analyze the cause of the failure, because dynamic routing protocols are usually used in larger networks, and they can automatically connect various network segments in the network. Of course, if a variety of dynamic routing protocols or multiple routing processes are used in the network, mutual introduction and filtering of routes will be involved. In fact, these can be analyzed by viewing the IP routing table on each device to quickly locate faults.

One thing to note here is that, try not to use static routing for routing configuration of the entire network, because static routing does not have the automatic advertisement function, and a static route can only be responsible for one-hop data forwarding, and Static routing is also one-way. Any communication between devices must be configured with a complete two-way routing. This is difficult to achieve in larger networks, and there may even be a large number of configuration errors or omissions.

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