Which header would have the sender's MAC address?

• A. IP header
• B. Ethernet header
• C. TCP header
• D. UDP header

Answer: (B)

The sender’s MAC address is part of the data-link layer, identifying devices on the local network. In Ethernet frames, the frame header carries both the destination MAC and the source MAC addresses. The IP header, by contrast, holds the sender’s and recipient’s IP addresses, which are logical addresses used across networks. TCP and UDP headers contain port numbers and control information, not hardware addresses. Because MAC addresses are tied to the local link and don’t traverse routers, they appear in the data-link (Ethernet) header that sits before the IP header. Therefore, the header that would contain the sender’s MAC address is the Ethernet header.