Explain the OSI model — and which layers do TCP and IP operate at?

The OSI model has 7 layers: Physical, Data Link, Network, Transport, Session, Presentation, Application. IP operates at Layer 3 (Network — handles addressing and routing between networks). TCP operates at Layer 4 (Transport — handles connection-oriented reliable delivery). UDP also at Layer 4 (connectionless). Memorising this is non-negotiable for any networking interview.

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