In a multi-stack configuration there can be duplication of interface indices. CINET inserts its transport driver index, TdIndex, into the upper halfword of all output interface indices to identify the interfaces uniquely. On input interface indices, the upper halfword is used to select a stack, and is cleared before the information is passed on to the stack. Each stack's TdIndex value is passed to it in PfsiTdIndex, but the stack does not have to do anything with the value.

For more information about the transport driver index, see the discussion of the SIOCGIFNAMEINDEX ioctl command in w_ioctl (BPX1IOC, BPX4IOC) — Control I/O in z/OS UNIX System Services Programming: Assembler Callable Services Reference.