The first two fields in an IPv4 header are as follows:

• Version 4-bit: This field value indicates the version of IP that is in use. Many devices support both IPv4 and IPv6. Therefore, it's important to obtain the version, so the device knows how to treat the traffic. In frame 1, we see Version: 4.
• Header length 4-bit: The header length is in multiples of four bytes, and is equal to the base header and any options. Although the length can vary (due to options), the minimum value must be five, which equals a header length of 20 bytes. In frame 1, the value shows Header Length: 20 bytes (5).

After these two fields, we see a field called DiffServ. Although the IPv4 header is shown in the Type of Service graphic lists, Wireshark will decode an IPv4 Type of Service (TOS) field as a DiffServ field, which is covered in the next section.