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Retrieve segment retransmission and reset connection counts for a line



Starting in IBM i 7.5, the number of segment retransmissions and reset connections for a physical line can now be retrieved to help assess the health of the network behind an interface.


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The TCP protocol is designed to guarantee delivery of data sent over a connection.  If a packet is lost, it will be retransmitted.  Additionally, if a connection gets reset, TCP notifies the remote side of this condition.  While the retransmit and reset are not necessarily problems themselves because the protocol was designed this way, they could help flag a potential problem in your network.  Previously, this information could only be retrieved in the context of connections.
In IBM i 7.5, the List Physical Interface Data (QtocLstPhyIfcDta) API added 2 new fields to the IPv4 format, IFCD0100, and IPv6 format, IFCD0300, to return this information.  This API now returns the number of times a TCP connection has made a direct transition to the CLOSED state from either the ESTABLISHED state or the CLOSE-WAIT state and the number of TCP segments transmitted containing one or more previously transmitted octets.  For more information, see the List Physical Interface Data (QtocLstPhyIfcDta) API.

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Modified date:
05 May 2022