When the exit routine is not enabled, or if it is enabled and indicates that an alternate ALS can be selected, all entries in the ALS list, as well as any ALS returned by the exit routine, are evaluated by VTAM® to determine whether any of the ALS entries are APPN connections, and to determine which ALS is the first best. An ALS that is returned by the exit routine is considered for selection before entries in the ALS list are considered.

• If an APPN ALS is found, VTAM attempts to find a route through the APPN network to the logical unit. A route computed by topology and routing services might use the ALS returned by the exit routine.
• If transaction routing services is unable to find a route through APPN, or if no APPN ALS is found, the first ALS that is found that fits one of the following descriptions is selected and session setup, using LEN protocols, continues:
  • Active
  • Leased, and in the process of activation
  • Switched, and pending dial
  • Connectable, switched
• Otherwise, VTAM attempts cross-domain routing, which might be limited to APPN if the exit routine prohibits subarea cross-domain routing, based on return codes (see Final register contents).