When troubleshooting network failures, engineers often use a layered troubleshooting approach. Because all models follow the same basic premise, a model's higher-level structures can only work…

When troubleshooting network failures, engineers often use a layered troubleshooting approach. Because all models follow the same basic premise, a model's higher-level structures can only work properly when all of its lower-level structures work properly. Please match the following inspection items with the corresponding layers in troubleshooting network failures. For example, whether the TCP connection is established correctly, whether the port is open, etc., whether the interface protocol is UP, whether layer 2 addressing is normal, etc., whether the physical status of the interface is UP, whether the cables and connectors are normal, etc., whether the routing protocol works normally, etc.