When an independent LU acts as the primary LU by initiating a session, VTAM® and NCP must assign another network address to the PLU. The AUXADDR operand on the BUILD definition statement reserves this address pool. Because this is a predefined pool, you should know the maximum number of concurrent PLU sessions that can be established by all independent LUs that are attached to that NCP. Otherwise, session establishment for an independent LU, acting as the primary LU, fails when the pool is exhausted.