/* * Given a LISTEN socket and an inbound SYN request, add * this to the syn cache, and send back a segment: * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK> * to the source. * * IMPORTANT NOTE: We do _NOT_ ACK data that might accompany the SYN. * Doing so would require that we hold onto the data and deliver it * to the application. However, if we are the target of a SYN-flood * DoS attack, an attacker could send data which would eventually * consume all available buffer space if it were ACKed. By not ACKing * the data, we avoid this DoS scenario. */