The Protocol Number Offset is located in which byte of the IP header?

The Protocol Number Offset is located in which byte of the IP header?

• A. 7th
• B. 8th
• C. 10th
• D. 9th

Answer: (D)

In IPv4, the Protocol field is a single octet that indicates the next header’s protocol (for example, 6 = TCP, 17 = UDP, 1 = ICMP). It appears after Time to Live in the header. If you count bytes from the start of the header using 1-based numbering, this Protocol field is the 9th byte. The 8th byte is Time to Live, and the 10th is the Header Checksum, so the Protocol number indeed sits in the 9th position.

In IPv4, the Protocol field is a single octet that indicates the next header’s protocol (for example, 6 = TCP, 17 = UDP, 1 = ICMP). It appears after Time to Live in the header. If you count bytes from the start of the header using 1-based numbering, this Protocol field is the 9th byte. The 8th byte is Time to Live, and the 10th is the Header Checksum, so the Protocol number indeed sits in the 9th position.