The IPv4 header has several fields, as shown in the following diagram:
IPv4 header
Some of the fields are rarely used, such as those that deal with fragmentation. Others provide information that can help with troubleshooting, such as the address fields when resolving network conflicts.
To examine an IPv4 header, open bigFlows.pcap, and go to frame 1, as shown here:
bigFlows frame 1—IPv4 header
The following section will list each field, and how many bits or bytes are used in each field, along with information on what each field represents. We'll start with the version and length fields.