The begin function of the directory services management exit can be activated by VTAM® initialization or by issuing a MODIFY EXIT,ID=ISTEXCDM,OPTION=ACT command. See z/OS Communications Server: SNA Operation for more information about this command.

The begin function is required if you write this exit routine; all other functions are optional. This function is processed during exit initialization before any of the other functions are processed. During the begin function processing, the exit selects the other functions to process. The exit is invoked for only those functions specified by your routine.

The address of the exit options is passed to the exit routine only during begin processing. The exit options field indicates the functions that the exit routine supports. This field is modified by the exit routine during processing of the begin function.

The address of the border node and interchange node options is also passed to the exit routine during begin processing. The border node and interchange node options field provides control information relating to the border node and interchange node selection functions of the exit routine. Bit definitions are described in Table 1.

If errors occur while processing the begin function, VTAM deactivates the exit and no functions are supported. The APPN network continues as if no exit routine exists. All search requests are authorized until the exit is reactivated.

If the exit return code is greater than X'7F', VTAM ignores any options you specified and issues error message IST985I.