Internet Protocol (IP)

The Internet Protocol is the core of the TCP/IP suite. It wraps data in packets, labels each with a logical source and destination address, and passes them from router to router across interconnected networks until they arrive. IP is connectionless and best effort: it does not set up a session, confirm delivery or put packets back in order. Those jobs belong to protocols above it, chiefly TCP, while UDP leaves them undone. Version 4 is defined in RFC 791 and version 6 in RFC 8200; IPv4 and IPv6 differ mainly in address size and header design.

IP sits at layer 3 of the OSI model and the Internet layer of the TCP/IP model, with ICMP beside it reporting delivery problems. Its security gap is simple to state: nothing in IP itself authenticates the source address or protects the contents. That is why address spoofing is possible, and why IPsec was designed to add confidentiality, integrity and origin authentication at the same layer.

Exam relevance: questions in this area tend to turn on the layer IP works at, the difference between its logical addresses and hardware MAC addresses, and the point that reliable delivery comes from TCP rather than from IP. A scenario that relies on a forged source address is likely to be testing this missing authentication.