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The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Transport Layer Protocols            9  Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)                 9  TCP/IP Transmission Control Protocol (TCP)                      9  TCP Basic Operation: Connection Establishment, Management and Termination

TCP Connection Establishment Sequence Number Synchronization and Parameter Exchange 1 2 3 TCP Connection Termination

Handling Reset Segments

When a device receives a segment with the RST bit sent, it tells the device to reset the connection so it can be re-established. Like all segments, the reset itself must be checked to ensure that it is valid (by looking at the value of its Sequence Number field). This prevents a spurious reset from shutting down a connection. Assuming the reset is valid, the handling of the message depends on the state of the device that receives it:

• If the device is in the LISTEN state, the reset is ignored and it remains in that state.
  
  
• If the device is in the SYN-RECEIVED state but was previously in the LISTEN state (which is the normal course of events for a server setting up a new connection), it returns to the LISTEN state.
  
  
• In any other situation, the reset causes the connection to be aborted and the device returns to the CLOSED state for that connection. The device will advise the higher-layer process using TCP that the connection has been closed.

TCP Connection Establishment Sequence Number Synchronization and Parameter Exchange 1 2 3 TCP Connection Termination