Final answer:
In the TCP/IP model, the internet layer (Layer 2) is used to inspect and monitor the flow of traffic across different networks.
Step-by-step explanation:
The layer in the TCP/IP model used to inspect the flow of traffic across a network is Layer 2, the internet layer. This layer is responsible for moving packets across network boundaries, and it handles the routing of Internet traffic. This includes the use of routing protocols to select the best path through the network to the destination. When seeking to inspect or monitor the flow of traffic, tools and protocols operating at this layer can track the movement of data packets between devices on different networks.