Which of the following values indicates UDP in the IPv4 header 'Protocol' field?

The value that indicates UDP (User Datagram Protocol) in the IPv4 header's "Protocol" field is 17. This field is used to specify the protocol used in the data portion of the IP packet. Each protocol defined at this level is assigned a unique number.

In this context:

• The value 1 represents ICMP (Internet Control Message Protocol).

• The value 6 is designated for TCP (Transmission Control Protocol).

• The value 89 is assigned to EGP (Exterior Gateway Protocol).

Understanding this numbering system is essential when analyzing network packets, as the protocol field helps systems identify how to process the data contained within the packet. Therefore, when examining the IPv4 header, seeing the number 17 tells you that the transport layer protocol in use is UDP, which is known for its low overhead and connectionless service, often used for applications where speed is critical, and loss of data is permissible.