When tcp performs a three-way handshake, the first step is that the client sends a syn request, the server returns syn+sck, and the client responds to sck

When the syn request times out, tcp will timeout retransmission, and the number of retransmissions can be viewed here cat /proc/sys/net/ipv4/tcp_syn_retries

 

 You can see that the number of retransmissions is 6 

 

Each timeout time is 1 second, 2 seconds, 4 seconds, 8 seconds, 16 seconds, 32 seconds

Use telnet to test a non-existent ip and port 

telnet 222.222.222.222 80

 Use tcpdump to view the retransmission phenomenon

tcpdump -i any port 88

 

 It can be seen that after the first connection failed, it was retransmitted 6 times

The interval time is 1 second, 2 seconds, 4 seconds, 8 seconds, 16 seconds, 32 seconds