TCP/IP

The layered protocol suite the internet runs on, named for its two core protocols.

TCP/IP is the four layer suite (link, internet, transport, application) that carries essentially all enterprise traffic, named after the two protocols that do the most work: IP for addressing and routing between networks, TCP for reliable ordered delivery within a connection. Security controls map onto its layers, which is why the model matters on the exam: IPSec protects at the internet layer, TLS at the transport boundary, and application firewalls inspect at the top. Contrast it with the seven layer OSI model, which is the reference used for describing where a control sits.