The three-way handshake is a cornerstone of the TCP suite:

SYN, SYN/ACK, ACK. SYN is the outgoing connection REQUEST from client to server. ACK is the acknowledgement of the server back to the client, saying that yes I hear you, let’s open a connection. SYN/ACK is the final connection, and allows the two to speak.

The problem is that this can be USED as a very basic type of DENIAL of Service Attack. The client opens up the SYN connection, the server RESPONDS with the SYN/ACK, but then the client sends another SYN. The server treats this as a new connection request and keeps the previous connection open. As this is repeated over and over many times very quickly, the server quickly becomes saturated with a huge number of connection REQUESTS, eventually overloading its ability to connect to legitimate users.

The three-way handshake is a cornerstone of the TCP suite:

SYN, SYN/ACK, ACK. SYN is the outgoing connection request from client to server. ACK is the acknowledgement of the server back to the client, saying that yes I hear you, let’s open a connection. SYN/ACK is the final connection, and allows the two to speak.

The problem is that this can be used as a very basic type of Denial of Service Attack. The client opens up the SYN connection, the server responds with the SYN/ACK, but then the client sends another SYN. The server treats this as a new connection request and keeps the previous connection open. As this is repeated over and over many times very quickly, the server quickly becomes saturated with a huge number of connection requests, eventually overloading its ability to connect to legitimate users.