Early on, scientists realized that IPv4's 32-bit address space would be exhausted. Although no one had an exact date, plans were made to replace IPv4 with an improved version, IPv6. In 1998, the IPv6 RFC was published and can be found at https://www.ietf.org/rfc/rfc2460.txt.

IPv6 has a number of enhancements, including the following.

• Streamlined header: Although the header is larger, due to the expanded address space, it is more streamlined.
• Flow label: In IPv6, there is a flow label. The field value is available for identifying streams that require specialized treatment, such as real-time traffic.
• Support for extensions and options: While IPv4 can add options, IPv6 does so with more ease. IPv6 provides the ability to add options, such as fragmentation, which has parameters to fragment the data, and hop by hop, which ensures that all devices in the path read the option.

The IPv6 header has room for the larger address spaces. However, as shown in the following diagram, the header is streamlined, in that there are not as many field values:

To follow along and examine an IPv6 header, open bigFlows.pcap, and go to frame 347. The IPv6 header is as shown in the following screenshot:

Note that IPv6 addresses are significantly larger as they are 128-bit as opposed to 32-bit for an IPv4 address. The address is shown using hexadecimal notation, as opposed to dotted decimal notation, which is used in IPv4.

In the next section, we'll review each field in IPv6 and the number of bits or bytes each field contains, along with information on what each field represents.