Denial of service type attacks are attacks where the nature of a system used to establish communication sessions is exploited to prevent the establishment of sessions. For example, to establish a Transmission Control Protocol (TCP)/Internet Protocol (IP) communication session, a three-way handshake is performed between communication endpoints. When a connection request is received, resources are allocated towards establishing the communication session. Malicious entities can attack the handshake by repeatedly only partially completing the handshake, causing the receiving endpoint to run out of resources for allocating towards establishing sessions, thus preventing legitimate connections. Illustrated embodiments overcome such attacks by delaying allocating resources until after the three-way handshake is successfully completed.