MRP see only the stock available and the requirements on nettable warehouses and generates the purchase/production advices only on the main warehouse of the items.
You should create a bill of distribution in order to define the replenishment rules, for the items involved, from the main warehouse, where the items are produced/purchased, to the no nettable warehouse.
DRP generates the distribution orders, based on the bill of distribution and taking in account the requirements generated from the sales order lines on no-nettable warehouses, that are the input for the next running of MRP.
I hope this can help you. Available for any further explanation.