An in-depth study on the problem of three-way handshake in TCP

< H2 > I know the process and basis of the three-way handshake. You don"t have to explain the basic concepts to me < / H2 > < hr >
the question is why the second handshake cannot be done
1. The information sent from the client to the server is delayed for a long time in the network. After receiving the message, the server returns a confirmation message, but at this time the connection of the client is nearly closed, but the server still waits all the time, which will cause a waste of server resources

this kind of understanding

2. The information transmitted from the client to the server is delayed for a long time in the network. after receiving the message, the server returns the confirmation message, but the client has abandoned the first connection and sent the request for the second connection. when the client receives the request, it will think that this is the confirmation of the second request, so as to establish the connection.

OK, that"s the problem. When sending a connection request and confirming a connection request, we will send the sequence number and the confirmation number. Assuming that the sequence number of the first request sent by the client is x, then the confirmation number in the packet in which the server returns the confirmation information should be xreply 1, and the sequence number of the second connection request sent by the client will obviously not be x, assuming y. Then when the client receives the confirmation number xroom1 in the confirmation message returned by the server, it should not establish a connection, because he needs to wait for a confirmation number of yroom1.
then this second problem should not exist.
my understanding of tcp is only conceptual, and I have not actually done any research on tcp, so there may be some problems in understanding. I hope you can point out.
I think the possible answer:
1. The client does not confirm the confirmation number, but why?
2. Both requests have the same sequence number (should not be possible, randomly generated)
3. This problem does not exist

/ / 2019.9.16 still not clear about the second case
still not clear

Tcp tcp-ip Network
Mar.29,2021

https://102.alibaba.com/detai. you can go and have a look. I hope it can help you 1

1 TCP provides reliable links and two handshakes. The client can confirm that the data sent to the server can be received by the server, and the server can also receive the data from the server, but the server does not know whether the data sent to the client can be received by the client. So you need a three-way handshake

2, "it took a long time to arrive in the network", which means your network is too bad, TCP handshake failed. Need to improve the network

the foundation of TCP needs to be strengthened.

generally speaking, there are two places where different TCP sessions can be distinguished

  1. sequence number
    usually the initial sequence number of both sides of the connection is a random number and is unpredictable.
    exception: in the event of a SYN flood attack, the server may use a special number as the serial number, details https://en.wikipedia.org/wiki.
  2. connection port of client
    most clients use dynamic (local) ports assigned by the operating system, which are theoretically different for each connection.

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