IPv4 versus IPv6

IPv4 versus IPv6
9.2.8 This page will compare IPv4 and IPv6.


When TCP/IP was adopted in the 1980s, it relied on a two-level addressing scheme. At the time this offered adequate scalability. Unfortunately, the designers of TCP/IP could not have predicted that their protocol would eventually sustain a global network of information, commerce, and entertainment. Over twenty years ago, IP Version 4 (IPv4) offered an addressing strategy that, although scalable for a time, resulted in an inefficient allocation of addresses.

The Class A and B addresses make up 75 percent of the IPv4 address space, however fewer than 17,000 organizations can be assigned a Class A or B network number. Class C network addresses are far more numerous than Class A and Class B addresses, although they account for only 12.5 percent of the possible four billion IP addresses.

Unfortunately, Class C addresses are limited to 254 usable hosts. This does not meet the needs of larger organizations that cannot acquire a Class A or B address. Even if there were more Class A, B, and C addresses, too many network addresses would cause Internet routers to come to a stop under the burden of the enormous size of routing tables required to store the routes to reach each of the networks.

As early as 1992, the Internet Engineering Task Force (IETF) identified the following two specific concerns:

• Exhaustion of the remaining, unassigned IPv4 network addresses. At the time, the Class B space was on the verge of depletion.

• The rapid and large increase in the size of Internet routing tables occurred as more Class C networks came online. The resulting flood of new network information threatened the ability of Internet routers to cope effectively.

Over the past two decades, numerous extensions to IPv4 have been developed. These extensions are specifically designed to improve the efficiency with which the 32-bit address space can be used. Two of the more important of these are subnet masks and classless interdomain routing (CIDR), which are discussed in more detail in later lessons.

Meanwhile, an even more extendible and scalable version of IP, IP Version 6 (IPv6), has been defined and developed. IPv6 uses 128 bits rather than the 32 bits currently used in IPv4. IPv6 uses hexadecimal numbers to represent the 128 bits. IPv6 provides 640 sextrillion addresses. This version of IP should provide enough addresses for future communication needs.

Figure shows an IPv4 address and an IPv6 address. IPv4 addresses are 32 bits long, written in decimal form, and separated by periods. IPv6 addresses are 128-bits long and are identifiers for individual interfaces and sets of interfaces. IPv6 addresses are assigned to interfaces, not nodes. Since each interface belongs to a single node, any of the unicast addresses assigned to the interfaces of the node may be used as an identifier for the node. IPv6 addresses are written in hexadecimal, and separated by colons. IPv6 fields are 16 bits long. To make the addresses easier to read, leading zeros can be omitted from each field. The field :0003: is written :3:. IPv6 shorthand representation of the 128 bits uses eight 16-bit numbers, shown as four hexadecimal digits.

After years of planning and development, IPv6 is slowly being implemented in select networks. Eventually, IPv6 may replace IPv4 as the dominant Internet protocol.

This page concludes this lesson. The next lesson will explain how IP addresses are obtained. The first page will discuss Internet addresses.