Using the NNSPREF start option

The NNSPREF start option gives the end node the ability to dynamically switch CP-CP sessions from the current network node server (NNS) to a different (preferred) NNS. This switch occurs automatically in either of the following circumstances:

A physical connection is successfully established between the end node and the preferred NNS.
The end node operator manually modifies the NNS preference from the name of one adjacent network nodes to the name of another adjacent network node (NN). In this case, a physical connection to the NN that is taking over the NNS function for the end node must exist.

If you do not specify NNSPREF, or specify NNSPREF with a value of NONE (the default), dynamic NNS switching is not enabled. You can modify NNSPREF using the MODIFY VTAMOPTS command. The value specified on MODIFY NNSPREF effectively gets dynamically added to the existing NETSRVR list table that is active. (To display the value of NNSPREF, use the D NET, VTAMOPTS,OPTION=NNSPREF command.) For more information about the DISPLAY VTAMOPTS command, see z/OS Communications Server: SNA Operation.