How does the Protocol field affect IPv4 packet processing?

• A. It tells the upper-layer protocol carried in the payload
• B. It specifies the destination host
• C. It indicates routing metric
• D. It carries the DSCP value

Answer: (A)

The Protocol field identifies which upper-layer protocol is carried in the IP payload, so the IP layer knows how to hand the data to the correct transport-layer handler (for example, TCP, UDP, or ICMP). It’s an 8-bit value with common numbers like 6 for TCP, 17 for UDP, and 1 for ICMP, guiding the receiving stack on how to interpret and process the payload. The destination host is determined by the Destination IP address, routing decisions are separate, and DSCP QoS markings live in a different field, not the Protocol field.