15.12.3 What Is the Difference Between IPv4 and IPv6?
- What Is the Internet Protocol?
- Why Was IPv4 Developed?
- Why Did IPv4 Run Out of Addresses?
- How Was the Problem Delayed?
- Why Was IPv6 Developed?
- How Are IPv4 and IPv6 Addresses Written?
- Is IPv6 Only About More Addresses?
- What Is the IPv6 Next Header Field?
- Are IPv4 and IPv6 Compatible?
- Will IPv6 Replace IPv4?
- Why Is IPv6 Important for the Future?
- What Should You Remember?
Short Answer
Internet Protocol Version 4 (IPv4) and Internet Protocol Version 6 (IPv6) perform the same fundamental function—they provide logical addresses that allow information to be delivered across interconnected networks. The principal difference is that IPv6 uses a much larger address space than IPv4, allowing virtually unlimited numbers of Internet-connected devices. IPv6 also introduces a simpler packet header and several architectural improvements that make the Internet more scalable and easier to manage.
What Is the Internet Protocol?
The Internet Protocol (IP) is the foundation of modern internetworking.
Whenever information is transmitted across the Internet, it is divided into small packets. Each packet carries an IP address identifying both its source and its destination. Routers examine these addresses to determine the path each packet should follow through the network.
Without IP, the Internet could not function.
Why Was IPv4 Developed?
IPv4 was developed during the late 1970s and became the standard Internet Protocol during the early 1980s.
At that time, the Internet connected only a relatively small number of universities, research laboratories, and government organizations. IPv4 uses a 32-bit address, allowing approximately 4.3 billion unique addresses. When the protocol was designed, this seemed far more than anyone would ever need.
As history has shown, that assumption proved to be overly optimistic.
Why Did IPv4 Run Out of Addresses?
The rapid growth of the Internet changed everything.
During the following decades the Internet expanded to include:
- personal computers;
- mobile phones;
- tablets;
- smart televisions;
- cloud computing;
- industrial control systems;
- connected vehicles; and
- billions of Internet of Things (IoT) devices.
Each of these devices required an IP address.
Although four billion addresses sounds like a very large number, the available address space was gradually exhausted as Internet usage expanded worldwide.
How Was the Problem Delayed?
Engineers introduced several techniques to extend the useful life of IPv4.
One of the most important was Network Address Translation (NAT). Instead of assigning every device its own public Internet address, NAT allows many devices to share a single public IPv4 address. For example, a typical home may contain:
- several computers;
- multiple smartphones;
- tablets;
- smart speakers;
- security cameras; and
- streaming devices.
Internally, each device uses its own private IP address. Externally, they all appear to communicate through the single public address assigned to the broadband router.
NAT has significantly delayed IPv4 address exhaustion and remains widely used today.
Why Was IPv6 Developed?
Although NAT extended the life of IPv4, it did not solve the underlying problem.
A new version of the Internet Protocol was therefore developed.
IPv6 increases the address size from 32 bits (IPv4) to 128 bits (IPv6). This seemingly simple change produces an astonishing increase in the number of available addresses.
Instead of approximately 4.3 billion addresses, IPv6 provides approximately 340 undecillion addresses.
This number is so enormous that it is effectively impossible to exhaust using any foreseeable communication technology.
How Are IPv4 and IPv6 Addresses Written?
IPv4 addresses are written as four decimal numbers separated by periods. For example 192.168.10.25.
IPv6 addresses are much longer and are written in hexadecimal notation using eight groups separated by colons. For example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334. Because long sequences of zeros occur frequently, IPv6 provides rules that allow addresses to be abbreviated into a much shorter form.
Although the notation looks unfamiliar at first, computers process both address formats in exactly the same way.
Is IPv6 Only About More Addresses?
No.
The larger address space is the most obvious improvement, but IPv6 also introduces several architectural enhancements. These include:
- a simplified packet header;
- more efficient packet forwarding;
- improved automatic address configuration;
- better support for modern networking; and
- a more flexible extension-header structure.
These improvements simplify router operation while providing greater flexibility for future Internet development.
What Is the IPv6 Next Header Field?
One important innovation in IPv6 is the Next Header field.
Rather than including numerous optional fields within the main packet header, IPv6 uses a chain of extension headers. The Next Header field identifies the type of header that follows. For example, it may indicate:
- a transport protocol such as TCP or UDP;
- a Fragment extension header;
- a Routing extension header; or
- a security-related extension header.
Each extension header contains its own Next Header field, allowing routers and receiving computers to process optional information in a flexible and organized manner.
Are IPv4 and IPv6 Compatible?
Not directly.
An IPv4 device cannot automatically communicate with an IPv6-only device because the two protocols use different address formats. To ensure a smooth transition, many modern networks support both protocols simultaneously. This approach is known as dual-stack operation. A dual-stack computer or router can communicate using either IPv4 or IPv6, selecting whichever protocol is appropriate for the destination.
This has allowed IPv6 deployment to occur gradually without disrupting the operation of the existing Internet.
Will IPv6 Replace IPv4?
Eventually, yes—but the transition is taking much longer than originally expected.
Because NAT has allowed IPv4 to remain usable, many organizations have continued operating IPv4 networks while introducing IPv6 gradually.
Today:
- many Internet Service Providers support both protocols;
- most modern operating systems support IPv6 automatically;
- cloud services increasingly use IPv6; and
- mobile networks commonly employ IPv6 internally.
For the foreseeable future, however, both protocols are likely to coexist.
Why Is IPv6 Important for the Future?
The Internet continues to expand every year.
Future growth will include:
- billions of additional IoT devices;
- autonomous vehicles;
- smart cities;
- industrial automation;
- satellite Internet systems; and
- future communication technologies that have yet to be developed.
IPv6 provides an addressing architecture capable of supporting this continued expansion without the limitations imposed by IPv4.
In many respects, IPv6 was designed not simply to solve today's problems but to support the Internet for many decades to come.
What Should You Remember?
IPv4 and IPv6 perform the same basic function—providing logical addresses that allow routers to deliver packets across interconnected networks.
IPv4 established the modern Internet but is limited by its 32-bit address space. IPv6 overcomes this limitation through 128-bit addressing while introducing a simpler and more flexible packet structure.
Although IPv4 remains widely used, IPv6 provides the long-term foundation for the continuing growth of the global Internet. Together, the two protocols have enabled the Internet to evolve from a small research network into the world's largest communication system.
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