What header field is used to identify specific traffic flows in an IPv6 packet?

The Flow Label field in an IPv6 packet is specifically designed to identify and differentiate between various flows of traffic. It is a 20-bit field that enables the efficient handling of packets belonging to a specific flow, which can be beneficial for real-time applications like voice over IP (VoIP) or streaming media that require consistent delivery times.

When a device sets the Flow Label field, it allows routers along the path to recognize and prioritize packets that belong to the same flow, potentially bypassing more complex routing processes and ensuring quality of service.

The Traffic Class field is allocated for prioritization of packets but does not uniquely identify each traffic flow; it is used for Differentiated Services (DiffServ) for quality of service. The Payload Length field indicates the length of the data carried in the packet but does not provide any flow identification. The Next Header field indicates the type of the next header immediately following the IPv6 header but does not serve to group packets into specific flows.

Thus, the Flow Label is critical for flow identification and effective traffic management within IPv6 networks.