For orders using the All or None (AON) attribute, IB will typically route to the native exchange, or hold the order if the AON order type is not supported by the primary exchange. When held, IB will attempt to simulate the order as follows:
For US stock orders: The NBBO must qualify limit price AND the NBBO size must be equal to (or greater than) the order size + 1000 shares.
For US options orders: The NBBO must qualify limit price AND the NBBO size must be equal to (or greater than) the order size + 10 contracts.
For example, an AON order to buy 1500 shares of ABC at $10.00/share will be held until the NBO qualifies (is less than or equal to $10.00) and the NBO size is equal to or greater than 2500 shares.
The order will remain active until it either executes or is canceled. The AON attribute can be used in conjunction with the basic order types and all times in force.