TCP_QUICKACK (since Linux 2.4.4) Enable quickack mode if set or disable quickack mode if cleared. In quickack mode, acks are sent imme‐ diately, rather than delayed if needed in accordance to normal TCP operation. This flag is not perma‐ nent, it only enables a switch to or from quickack mode. Subsequent operation of the TCP protocol will once again enter/leave quickack mode depending on internal protocol processing and factors such as delayed ack timeouts occurring and data transfer. This option should not be used in code intended to be portable.