TCP half-open: Difference between revisions

Revision as of 13:01, 4 October 2006

Revision as of 13:02, 4 October 2006

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The TCP protocol has a three state system for opening a connection. First, the originating site (A) sends a [[SYN (TCP)|SYN packet]] to the destination (B). A is now half-open, and awaiting a response. B now updates its kernel information to indicate the incoming connection from A, and sends out a request to open a channel back (the SYN/ACK packet).

At this point, B is now "Halfhalf-open" (it has sufficient information to receive packets, but not enough to send packets back). Note that B was put into this state by another machine, outside of B's control.

Under normal circumstances (see [[denial-of-service attack]] for deliberate failure cases), A will receive the SYN/ACK from B, update its tables (which now have enough information for A to both send and receive), and send a final ACK back to B.