Transport Layer is the 4th layer in the ISO OSI model. It sits between the network layer and the Session layer. The transport layer provides transparent transfer of data between systems. One of the unique features of transport layer is end to end error recovery and flow control.

However, the transport layer suffers from certain vulnerabilities. Transport of data may face some difficulty in case there are differences in transport protocol implementation. Similarly, overloading of transport layer mechanisms such as port numbers limit the ability to effectively filter and qualify traffic. Transport layer also suffers from spoofing.

Since the transport layer deals with the transfer of data, a stateful inspection firewall placed can filter phony and illegal packets from entering the network. Transport layer has some controls like stronger transmission and session layer identification mechanisms to prevent attacks.

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