Unable to Establish Connection with Server (3)
Step 2: Open the scatter point details link and obtain the corresponding captured packets
Step 3: Ping + packet capture analysis (unable to establish connection Error corresponding analysis of TCP protocol-related packet information in the packet capture)
TCP connection establishment: A reliable communication channel is established through the TCP three-way handshake. The essence of a reliable channel is the sending and receiving of data. The main task of the three-way handshake is to enable both parties to confirm whether the sending and receiving functions of themselves and the other party are normal.
Common TCP filtering rules:
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2.
Overview of TCP three-way handshake:
First handshake: client->server: SYN packet
Second handshake: server->client: SYN+ACK packet
The third handshake: client->server: ACK packet
The normal three-way handshake packet capture is shown in the figure below:
First, use the packet capture tool to open the packet capture and enter tcp or ip.122.224.250.220 in the filter condition (directly entering tcp is filtered by protocol, and to accurately filter the packet information we want to analyze, we need to filter accurately and filter according to the monitoring target Hostip). From the packet capture, we can see from the packet capture that the client sends a SYN packet during the first handshake of TCP connection establishment, but never receives a SYN+ACK packet from the server (SYN+TCP Retransmission timeout and retransmission), combined with ping: 122.224.250.220 complete packet loss, preliminary analysis is that network exception caused the client to fail to successfully send network request, which resulted in the server not receiving the Request that the client sent a SYN packet to establish a connection, and finally failed to establish a connection.
Step 4: Instant Testing result (reproduction)
Use 8442796Probe and specify to access: 122.224.250.220 target Host and the result is normal.
Step 5: Solution
The feedback is that the Network link fluctuation caused the occasional resolution Exception, which has now returned to normal.