Figure 5-2 shows the IP header’s structure. The following sections discuss the fields of the IP header.
Figure 5-2. The structure of the IP header
The Version field is 4 bits long and is used to indicate the IP header version. A 4-bit field can have values from 0 through 15. The most prevalent IP version used today on organization intranets and the Internet is version 4, sometimes referred to as IPv4. The next version of IP is IPv6. All other values for the Version field are either undefined or not in use. For the latest list of the defined values of the IP Version field, see http://www.iana.org/assignments/version-numbers.