Linux Network Basics transport layer

TCP (Transport Control Protocol) three-way handshake: the first handshake, the SYN field is 1, and other flag fields are TCP (Transport Control Protocol)
Three-way handshake: the first handshake, the SYN field is 1, the other flag field is 0, the second handshake, the SYN field is 1, the ACK field is 1, and the other is 0. The third handshake, SYN = 0 ACK = 1, and other fields are 0.
Four waves, the first wave, the request to interrupt the transport side FIN = 1, the second wave, the interrupted side ACK = 1, FIN = 0, indicating that the request was interrupted, for the third wave, the victim FIN = 1 and the fourth wave, the victim FIN = 0 and ACK = 1, indicating that the victim received the interrupt message.

FTP port numbers 21 and 20
TFTP Port 69
Telnet port 23
SMTP port number 25
POP3 port 110
HTTP port 80
DNS port number 53