Analysis of RST/PSH and other state problems

Urg:urgetpointer is valid (Emergency pointer field value is valid)

SYN: Indicates a connection is established

FIN: Indicates closing the connection

ACK: Indicates a response

PSH: Indicates data data transfer

RST: Indicates a connection reset.

Question 1:

1) After three-time handshake

2) client sends PSH

3) Timeout 200ms not received ack,client send TCP retransmission retry

4) The server receives the TCP retransmission and immediately returns the RST, possibly the server side has disconnected the connection.

5) The client receives the RST and immediately reports connection reset by peer. The RST may be returned by the corporate intranet gateway.

Normally, when the client sends PSH, the server returns an ACK immediately

6) through tracert-d XX. Xx. Xx. The XX command tracks the route through which the destination IP is accessed. However, some gateways block ICMP probes and cannot detect the routes they are routed through.