TCP连接请求：接收方返回RST包的原因分析

There could be several reasons why the receiving side returns an RST (Reset) packet in response to a TCP connection request:

Closed Port: The destination port on the receiving side is closed or not being listened to by any service. In such cases, the receiving side sends an RST packet to indicate that the requested port is not available.
Firewall or Security Settings: The receiving side may have a firewall or security settings that block incoming connection requests. The firewall detects the incoming TCP SYN packet and responds with an RST packet to terminate the connection attempt.
SYN Flood Protection: The receiving side may have SYN flood protection mechanisms in place to prevent denial-of-service attacks. If it receives a large number of SYN packets within a short period, it may respond with RST packets to terminate those connections and protect its resources.
Connection Rejection: The receiving side may reject the connection request for various reasons, such as reaching its maximum connection limit, insufficient resources, or policy restrictions. In such cases, it sends an RST packet to inform the requesting side about the rejection.
Network Issues: There could be network issues or misconfigurations that cause the RST packet to be sent erroneously. This could include routing problems, packet loss, or other network disruptions.

It is important to note that the RST packet indicates that the connection request was rejected or terminated, and the specific reason may vary depending on the configuration and behavior of the receiving side. Network administrators can analyze network logs or capture packets to identify the exact cause of the RST packet in a particular scenario.