Suppose host H1 is looking to make a TCP connection with H2 and sending a SYN for the 1st step of 2-way handshake. H1 then isn't hearing back in timeout and is sending a seond SYN to H2.
Then, H1 is hearing back on both of these SYNs. What does H1 do in this case-- which one of these two does it ACK as the 3rd step of handshake, the first SYN+ACK from H2 or the second? The two SYN+ACK have 2 different Iitial Sequence Numbers (ISNs) of H2. They also have different ACKs-- H1 sent 2 different ISNs in its two SYNs.
//---------------------------------------------------
From another point - in such a case, what does H2 do? So - H2 received an SYN and sent SYN+ACK in response to it. After a while, H2 received another SYN+ACK from H1. What does H2 do in this case:
- send SYN+ACK to the second SYN as well? in this case, how does H2 know which SYN (the ISN of H1) is the one for this connection?
or
- ignore the second SYN. But then, H1 timed out as well-- it didn't hear back any since it send the previous SYN+ACK.
How is this handled in TCP?
