IPv4 vs. IPv6: A Comprehensive Guide To The Two Internet Protocols

IP address, or Internet Protocol address, is a numerical label assigned to internet-connected devices, including laptops, printers or mobile devices on a particular network. The first version of the Internet Protocol was introduced in 1973, but IPv4 was the first to be used widely.

When IPv4 emerged, no one could have imagined the scale of the internet today. Unsurprisingly, as the internet expanded, the pool of unallocated IPv4 addresses drained fast, and in 2011, IANA (Internet Assigned Numbers Authority) officially exhausted its IPv4 free pool. 

By this time, IPv6 was already introduced as an alternative with an astonishing number of IP addresses. While IPv6 adoption has steadily increased over the years, IPv4 still plays a central role across many networks, and both protocols continue to coexist.

To understand IPv4 vs. IPv6, we need to look at how these Internet Protocols emerged, what benefits they offer, and how the two protocols differ in practice.

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What is IPv4?

IPv4 stands for Internet Protocol version 4, and it was first introduced in 1981 by DARPA as a connectionless protocol, later standardized by the IETF. An IPv4 address is 32 bit-long and is made up of four octets written in decimal digits between 0-255 and separated by dots. Each block represents one unique byte.

For example: 1.2.3.4 (ISP: APNIC Pty Ltd.) or 208.65.153.238 (ISP: Youtube LLC).

In total, there are 4,294,967,296 IPv4 addresses, and this number is set, meaning that it cannot expand. Forty years later, we are still dependent on IPv4, but the original creators failed to imagine the scale of the internet in the 2020s. 

Back in the 1980s, 4.29 billion might have sounded like an unlimited number. Today, we are dealing with IPv4 exhaustion across regional registries, with continued demand being met through address transfers, secondary markets, and leasing.

RIPE NCC, one of the five Regional Internet Registries that allocate internet number resources, ran out of IPv4 in November 2019. When the pools of IPv4 addresses drain, RIRs no longer have the resources to allocate or assign. 

However, the need for IPv4 resources has not diminished. While IPv6 already offers far more unique addresses, the transition from IPv4 remains complex due to compatibility requirements, legacy systems, and widespread dual-stack deployments.

Benefits of using IPv4

The IPv4 infrastructure has been around for decades and is now fully developed and optimized. IPv4 is the most widely deployed IP version to identify devices, which is not yet the case for IPv6.

Users of IPv4 don’t need to worry about upgrading their devices or finding experts who would take care of these upgrades. Working with this Internet Protocol version 4 is something that network operators are used to and don’t require additional training.  

In the past, there were concerns that IPv4 is not as secure as IPv6. While that might have been true at one point, the security of the infrastructure has been upgraded as well. Now, security systems are in place to ensure that IPv4 networks are just as secure, as long as they are appropriately configured.

The benefits:

• Set-in-place infrastructure
• Fully optimized networks
• Stable security 

What is IPv6?

IPv6 stands for Internet Protocol version 6, and it is the latest version of the Internet Protocol. It was introduced in 1995 by the Internet Engineering Task Force, and the exhaustion of IPv4 addresses was already evident by this point. Although the logical sequence suggests that IPv5 would precede IPv6, the so-called Internet Stream Protocol was never fully deployed.

An IPv6 address is 128 bits long, and while the first 64 bits represent the network portion, the last – the host portion. An IPv6 address comprises eight groups written in hexadecimal format using values between 0 and FFFF and colons. 

For example, 2001:4860:4860::8888 (Google LLC). The double-colon in this technical format indicates that the middle segments represent zeroes. The fully expanded version of this address is 2001:4860:4860:0000:0000:0000:0000:8888.

There are 340,282,366,920,938,463,463,374,607,431,768,211,456 (340 undecillion) IPv6 addresses in total. Needless to say, when we compare IPv4 vs. IPv6 by numbers, there is no comparison, and the size of this address space is much more suitable for today’s IoT world.

That said, although IPv6 has been available for decades and its adoption continues to grow, deployment remains uneven across regions, industries, and network environments.

According to Google, IPv6 connectivity availability among Google users is now close to 50% globally. Despite this progress, IPv4 remains essential for compatibility and connectivity across large parts of the internet.

Benefits of using IPv6

IPv6 plays a critical role in the future growth of the Internet, particularly as networks scale beyond IPv4’s limits. We will need to transition to IPv6 sooner or later, and when we do, we will not need to worry about IP address exhaustion due to numerous unique addresses available. At the moment, this is the most significant problem that the IPv4 infrastructure faces.

Complex configurations are the thing of the past with IPv6. While you need to assign IPv4 addresses for one system to communicate with other systems and perform firewall alterations, IPv6 offers stateless auto-configuration. During the process, the host finds an IPv6 router and requests a prefix, creates a link-local address and verifies that the address is unique.

The IPv6 infrastructure is also much more suitable for mobile networks. As the IoT (Internet of Things) continues to expand, the ability to assign globally unique IP addresses to a massive number of devices becomes increasingly important, and IPv6 was designed with this scale in mind.

The benefits:

• More unique IP addresses
• Stateless auto-configuration
• Mobile network-friendly

Key differences between IPv4 vs. IPv6

Both IPv4 and IPv6 identify devices on a network and relay information across it, unlike MAC addresses, which uniquely label individual network interfaces. Both versions support common transport protocols such as TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) and can offer similar performance in direct connections. Nevertheless, there’s more than one difference between IPv4 and IPv6. 

The comparison

As you can see, when it comes to comparing IPv4 vs. IPv6, there’s more than just the obvious numeric address vs. alphanumeric address difference. 

While both versions contain extension headers, the IP address header of each IP is different. 

The IPv4 infrastructure uses a subnet mask for every designated network, and the IPv6 infrastructure doesn’t use masks at all; it uses prefix lengths instead. 

You also need to configure a newly installed system with an IPv4 address, but that is optional for IPv6, which also offers autoconfiguration capabilities.

Network Address Translation (NAT) supports IPv4, and a single NAT address can mask non-routable addresses, but IPv6 uses direct addressing instead. This means that connection occurs at the IP layer, and IPv6 users don’t need to deal with port forwarding.

IPv4 also uses Dynamic Host Configuration Protocol (DHCP) to obtain IPs. However, IPv6 users don’t need to access a dynamic host configuration server because of permanent addresses.

It’s also pretty obvious that Internet Protocol security is stronger for IPv6 due to IPSec integration. Furthermore, compared to IPv4, Quality of Service (QoS) handling is more efficient in IPv6 networks.

Today, not all infrastructure solutions support the IPv6 protocol. Additionally, even if your company is fully IPv6 compliant, you will still need IPv4 to communicate with partners or clients who are not. As a result, there is a tendency to build dual infrastructures that can support both versions of the Internet Protocol.

The future of Internet Protocols

The long-term relationship between IPv4 vs. IPv6 remains shaped by coexistence rather than outright replacement. While IPv6 adoption continues to increase, it remains difficult to predict when, or even if, it will fully replace IPv4.

The future of IPv4

Although IPv4 internet addresses might be exhausted, we still have ways to go before IPv6 becomes the standard Internet Protocol. While we wait for the technology and internet service providers to catch up, we have no other option but to work with what we have. Luckily, what we have is convenient and familiar.

Unfortunately, while IPv4 continues to be the convention, we are left dealing with the lack of IPs, which seriously hinders the growth of businesses across the globe. Buying or selling IPs might seem like an obvious option, but it is not always the most flexible or cost-effective approach. Moreover, opportunities to acquire IPv4 addresses outright are increasingly limited and often come at a high cost. That same trade-off remains visible in IPv4 pricing in 2026.

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Reusing IP addresses helps build a sustainable internet that is not paralyzed by the lack of essential resources. Fortunately, plenty of IPv4 addresses are still unused.

With words from Cogent Communications Holdings, Inc. recognizing IP lease as a trustworthy business model and IP addresses – a valuable economic asset, it seems that IPv4 supply in the market might increase with those who were withholding their resources.

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The future of IPv6

While IPv6 may be the future of the internet, we don’t know yet when this future will come. Will we see IPv6 fully replace IPv4 by 2040? 2050? It isn’t reasonable to make such predictions at this time. At the end of the day, a complete transition away from IPv4 is unlikely in the foreseeable future, making coexistence and sustainable IPv4 use essential today.

Internet service providers (ISPs), mobile carriers and data centers will go on to fully adopt IPv6 at some point. However, for many organizations, the cost, complexity, and operational effort required for a full IPv6-only migration remain significant.

There’s also a lack of motivation to move from the existing infrastructure, especially since IPv4 and IPv6 can coexist. Dual IP stacking, tunneling and NAT64 can help achieve that.

• Dual IP stacking: Network hardware runs IPv4 and IPv6 simultaneously
• Tunneling: IPv6 data packets are encapsulated within IPv4 packets
• Network Address Translation-Protocol Translation: IPv4 packets are translated into IPv6 packets, or IPv6 packets are translated into IPv4 packets

All in all, IPv6 adoption continues to grow steadily, with mobile networks leading deployment. In the US, T-Mobile is close to routing 100% of web traffic using IPv6, while AT&T and Comcast are close behind with 80% and 74% routing, respectively. 

According to Google’s Per-Country IPv6 adoption statistics (May 2024), France is the number-one country in the world by IPv6 adoption at 75.02%, followed by Germany (73.3%), India (69.84%), Malaysia (66.52%) and Saudi Arabia (62.22%). The US is currently at 45.75%.

Conclusion

IPv6 may replace IPv4 one day, but that isn’t happening tomorrow. While IPv6 might be more mobile-network friendly, mandate IP security and provide a lot more IP addresses, IPv4 continues to play a central role on the internet today. 

Before IPv6 fully replaces IPv4, we will see both Internet Protocols coexisting. Right now, however, IPv4 addresses are exhausted at the registry level, and more companies run into the problem of being unable to scale due to IP address shortage. 

The good news is that a sustainable internet is no longer just a theoretical idea, and we can grow without relying solely on newly allocated IP addresses.

As long as there are unused IPv4 addresses, there will be someone in need of them. Now is the perfect time to put dormant IPs to use and alleviate the global IPv4 shortage.

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