Border node selection function (function code X'01')

This function is optional. If processed, when VTAM® builds a subnetwork routing list for sending a directed locate search to a border node or nonnative network node, VTAM forwards a copy of the subnetwork routing list to the exit.

The user exit can change the subnetwork routing list by:

Removing entries from the list
Reordering the entries in the list
Adding entries to the list
Replacing entries in the list

Modifying the subnetwork routing list might involve the physical movement of data within the storage. For example, to remove an entry from the list, the entries following the deleted entry must be moved to be contiguous with the entry before the deleted entry, and the number-of-entries count must be decremented by one.

In addition to modifying the subnetwork routing list, the exit can indicate that no border node search procedure should be attempted.

The user-written exit returns to VTAM with a return code:

Register 15:

Return code

X'00' (0): Border node searching is allowed using the subnetwork routing list returned by the exit.
X'04' (4): Border node selection was not performed. The original subnetwork routing list should be used.
X'08' (8): Border node searching is not allowed.

All other return codes are treated as return code X'04'.

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