Figure 2-8: Host RJ-11 IP Gateway: Network Interface Settings
TCP keep‐alive is a standard feature of TCP/IP that can be configured to automatically monitor the state of TCP connec‐ tions. If one end of an idle TCP connection is severed (like by a network or power failure), it is possible for the other end to remain open indefinitely. If a network host fails while it has an open TCP connection to one of the device server’s serial ports, that serial port might remain unavailable until it is manually reset.
The optional TCP keep‐alive feature sends special “keep‐alive” packets to the remote TCP host in order to detect the situation where the remote host fails. If a failure is detected, the TCP connection is reset to allow other hosts to access the serial port.
To enable TCP keep‐alives on serial‐related network connec‐ tions, enter the total time (in seconds) that you will allow TCP connections to remain idle before resetting them. The first keep‐alive packet will be sent after the connection has been idle for half of this total time. After that, four more TCP keep‐ alive packets will be sent at regular intervals until a TCP response is received from the remote host. If no response is received before the total keep‐alive time runs out, the TCP connection will be reset.
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