What is OSI Layer 4?

Understanding OSI Layer 4

Transport layer. Layer 4 of the OSI model ensures reliable end-to-end data delivery between applications providing services such as connection establishment flow control error recovery and segmentation/reassembly. It uses protocols like TCP connection-oriented and UDP connectionless. Security at this layer addresses issues like port scanning and denial-of-service attacks. Transport layer security is addressed in standards like NIST SP 800-53 ISO 27001 and various IETF RFCs. Organizations implement Layer 4 security through stateful firewalls port filtering TCP wrapper controls rate limiting and SYN flood protection. For example a security team might configure stateful firewalls to track connection states implement rate limiting to prevent SYN flood attacks and use port-based access controls to restrict access to services based on source/destination port numbers. Related terms TCP UDP Ports Stateful inspection Connection tracking Flow control SYN flood Session establishment.