Computer Networks PCCST501 Semester 5 KTU CS 2024 Scheme - Dr Binu V P

  SYN Flooding Attack A SYN flooding attack is a type of Denial-of-Service (DoS) attack that exploits the TCP three-way connection establishment process . The main idea is that the attacker sends a large number of SYN requests to a TCP server but does not complete the connection establishment. As a result, the server has to keep resources reserved for many incomplete connections. 1. Normal TCP Connection Establishment Normally, TCP establishes a connection using three steps: Client Server | | | -------- SYN --------------> | | | | <------ SYN + ACK ---------- | | | | -------- ACK --------------> | | | Connection established The three steps are: Client → Server: SYN Client requests a TCP connection. The client provides its initial sequence number. Server → Client: SYN + ACK Server accepts th...

  TCP Connection Establishment — Three-Way Handshaking TCP is a connection-oriented protocol . Before any application data is exchanged, the two TCP endpoints must establish a logical connection . The connection establishment process is called three-way handshaking . A useful way to understand it is: SYN → SYN + ACK → ACK The three messages synchronize the sequence numbers in both directions and confirm that both sides are ready for communication. 1. Why does TCP need connection establishment? TCP provides full-duplex communication , meaning both sides can send data simultaneously. Therefore, before data transfer begins, both TCP endpoints need to: agree to establish a connection, synchronize their sequence numbers, acknowledge each other's initial sequence number, communicate the receiver's available window size. TCP creates a logical connection , not a physical connection. The underlying IP protocol remains connectionless. IP simply delivers individual ...