The first three fields in an IPv6 header are as follows:

• Version 4-bit: This field indicates the IP version that is in use. In frame 347, we see version 6.

• Traffic class 8-bit: When sending data on the internet, some traffic requires special handling and prioritization. The traffic class field houses two (2) values, TOS and ECN:
  • TOS: The first 6-bit of this field is used to communicate what type of service is requested. TOS uses the same DSCP values as IPv4. Frame 347 uses the default value, Differentiated Services Codepoint: Default (0).
  • ECN: The last 2-bit of this field are used to indicate congestion on the network in the same way as IPv4. In frame 347, this value is Explicit Congestion Notification: Not ECN-Capable Transport (0).
• Flow label 20-bit: This is a new field that can be used to identify a specific flow of information in order to provide sequencing or request special handling by routers in the path. In frame 347, we can see Flow Label: 0x00000. In RFC 2460, Appendix A: Semantics and Usage of the Flow Label Field, there is an expanded discussion on the flow label. However, after two decades, the flow label is considered experimental, and is generally not used.

The next three fields deal with similar values found in an IPv4 header, but have subtle differences, as shown next.