Methods and systems for enabling security in transferring data from a single level MILS partition to the multiple level LAN. When a frame is received from an external stack via a network interface card, the frame contains a security classification, which is compared to the security classifications assigned to a plurality of internal stacks. Once a match is obtained, the frame is forwarded to the internal stack corresponding to the security classification in the frame assigned by the external stack. When a frame is received from one of the plurality of internal stacks, no security classification exists within the frame. A determination of the security classification assigned to the internal stack, which is then written into a security label in the frame. Once the security label is attached to the frame, the frame is sent to the external stack via a network interface card.