Which of the following IP header fields is used to distinguish IPv4 from IPv6 traffic?

The correct choice is the Version field, which plays a crucial role in identifying whether an IP packet is using IPv4 or IPv6. This field specifies the version of the Internet Protocol in use. In the case of IPv4, the version is indicated as '4', while for IPv6, it is indicated as '6'. This distinction is fundamental because it allows routers and network devices to process the packets according to the appropriate protocol specifications.

The Version field is essential for enabling compatibility and proper handling of packets across different versions of the Internet Protocol, ensuring that the right processing rules are applied. Without this field, network devices would be unable to determine how to interpret the information within the packet, which could lead to communication failures.

Other fields such as Type of Service, Identification, and Protocol serve different purposes. Type of Service is used to indicate the handling priority for the packet, Identification is utilized for fragment reassembly in IPv4, and Protocol specifies the encapsulated protocol within the IP packet. While these fields are important for packet forwarding and management, they do not serve the specific purpose of identifying the version of the IP protocol being used.