TCP is designed to take care of network link breaks. So when you disconnected from R1 by reconfiguring IP addresses, TCP connection did not break, instead it was re-transmitting to hear from remote end. Before the re-transmits timedout, you were able to establish communication. Here's further details.
SYN : SYN is only exchanged at first connection establishment, does not happen again during this scenario.
SEQ/ACK : During re-transmits, these numbers remain the same. These numbers are the next expected segment number. When you were disconnected, they were re-transmitted again and again until connection established.
Window Size : Frozen when you were disconnected. Window size changes during the course of TCP transactions depending on the available network/router resources, but at the time of disconnect, it was the one at last successful TCP transaction.
during re-transmits, the R1 is expecting recived the TCP packet with the old IP instead of new IP or R1 is able to recived the new connection with new IP and I am guessing the R1 will throw away the old TCP info because the IP changed
and since the IP changed, SYN should appear in new connection because the R1 can not recived the old TCP info anymore
Good point. But remember that TCP is not a Network layer protocol, so it does look at the network layer. So when IP changes, it's only the matter of a second or two when network layer re-establishes. During the time network layer is down, TCP keeps re-sending segments. Before TCP re-transmission times out, network layer re-establishes, and your telnet session restores. The SYN, ACK, Window size remains the same as I explained in my previous message.
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