The TCP connection management protocol sets a position for a classic Denial of Service (DoS) attack, called the SYN flooding attack. In this attack attacker sends a large number of TCP SYN segments, without completing the third handshaking step to quickly exhaust connection resources of the victim server. Therefore it keeps TCP from handling legitimate requests. This paper proposes that SYN flooding attack can be viewed metaphorically as result of an unfair scheduling that gives more opportunity to attack requests but prevents legal connections from getting services. In this paper, we present a scheduling algorithm that ejects the half connection with the longest duration, when number of half open connections reaches to the upper bound. The simulation results show that the proposed defense mechanism improves performance of the under attack system in terms of loss probability of requests and share of regular connections from system resources. تفاصيل المقالة