During the initial SyN handshake we see a "windows size" field in the trace file. Is that field sent by the client (sender) or the destination (server) ? My understanding is that the initial SYN in the beginning of the three way handshake is always started from the client (sender), is that correct ? asked 13 Aug '13, 19:45  Robbie S |
2 Answers:
Yes that is correct. "Active opener trying to connect to the Passive Listener" answered 13 Aug '13, 21:39  krishnayeddula |
The SYN is sent by the system that is initiating the TCP connection. That is usually, but not always, the client. For example, in FTP, the FTP client will initiate a connection to the FTP server on the command channel (port 21). Each system is both a sender and a receiver. The client sends commands, and the server sends responses. However, when files are uploaded or downloaded, a separate connection is established. In active FTP, the server connects to the client; in passive FTP the client connects to the server. Data flows in one direction only. Which system is the sender depends on whether the transfer is an upload or a download. Both systems send their window size. answered 13 Aug '13, 22:07  Jim Aragon |
