Which layer in the TCP/IP model is responsible for routing messages through an internetwork?

• A. Internet
• B. Transport
• C. Network Access
• D. Session

Answer: (A)

Routing across an internetwork is handled by the Internet layer of the TCP/IP model. This layer provides logical addressing with IP addresses and enables packets to move from one network to another by having routers examine the IP header and forward datagrams toward their destination, often across many hops and different networks. The Transport layer takes care of end-to-end delivery between applications (using TCP or UDP) but doesn’t route between networks. The Network Access layer handles delivering frames on a single local network and isn’t responsible for inter-network routing. In TCP/IP, there isn’t a separate Session layer; its responsibilities sit with the other layers, primarily the Transport and Application layers. So the Internet layer is the one that routes messages through an internetwork.