Which OSI layer is responsible for adding the IP header that contains the source IP address?

• A. Data Link Layer
• B. Application Layer
• C. Transport Layer
• D. Network Layer

Answer: (D)

Logical addressing and routing happen at the Network Layer, where the IP header is created to carry the source and destination IP addresses. This header enables routers to forward the packet toward its destination across multiple networks. The Data Link Layer handles local delivery on a single hop using MAC addresses and does not add IP headers. The Transport Layer adds its own header with port numbers and sequencing information, not IP addresses. The Application Layer deals with end-user data, not addressing. So the IP header that contains the source IP address is added at the Network Layer.