IPv4 vs IPv6: What UK Businesses Need to Know

The Internet Protocol — the fundamental addressing system that makes network communication possible — is undergoing the most significant transition in its history. IPv4, the protocol that has underpinned the internet since 1983, is running out of addresses. Its successor, IPv6, offers a virtually unlimited address space and several technical improvements, but adoption has been gradual and uneven. For UK businesses, understanding the difference between these two protocols, and planning for the transition, is becoming increasingly important.

This is not merely an academic concern for network engineers. The exhaustion of IPv4 addresses is already affecting businesses in tangible ways — from rising costs for IPv4 address space to compatibility issues with modern cloud services that are increasingly IPv6-native. Whether you run a small consultancy in Bristol or a growing technology company in London, the IPv4-to-IPv6 transition will affect your network infrastructure, your cloud strategy, and potentially your ability to do business with certain partners and customers.

This guide explains the key differences between IPv4 and IPv6, the current state of adoption in the United Kingdom, and the practical steps your business should take to prepare for a dual-protocol future.

Understanding the Fundamentals

Every device connected to a network — whether it is a laptop, a server, a printer, or a smart thermostat — needs a unique IP address to communicate with other devices. IPv4 uses 32-bit addresses, written as four groups of numbers separated by dots (for example, 192.168.1.100). This format provides approximately 4.3 billion unique addresses. When IPv4 was designed in the early 1980s, 4.3 billion seemed like more than enough for any conceivable future use. Nobody anticipated that within a few decades, billions of people would carry internet-connected devices in their pockets, and that everything from refrigerators to light bulbs would need IP addresses.

IPv6 uses 128-bit addresses, written as eight groups of four hexadecimal characters separated by colons (for example, 2001:0db8:85a3:0000:0000:8a2e:0370:7334). This provides an astronomically larger address space — enough to assign a unique address to every grain of sand on Earth and still have addresses left over. Beyond the larger address space, IPv6 also introduces several technical improvements over IPv4.

Why IPv4 Addresses Are Running Out

The Internet Assigned Numbers Authority (IANA) allocated its last blocks of IPv4 addresses to the Regional Internet Registries back in 2011. RIPE NCC, which manages IP address allocation for Europe and the UK, exhausted its final /8 block in November 2019. Since then, new IPv4 addresses have only been available through a waiting list for very small allocations (a single /24 block of 256 addresses) or through the secondary market, where organisations buy and sell existing address space.

This scarcity has created a thriving market for IPv4 addresses. Prices have risen steadily from a few dollars per address a decade ago to over £35 per address today. For a UK business that needs a /24 block (256 addresses), that represents a cost of approximately £9,000 — just for the addresses themselves, before any infrastructure costs. This makes IPv4 address space an increasingly expensive and finite resource.

The workaround that has sustained IPv4 for the past two decades is Network Address Translation (NAT), which allows multiple devices on a private network to share a single public IPv4 address. NAT has been remarkably effective, but it introduces complexity, breaks certain applications, and creates performance overhead. It is a sticking plaster, not a solution — and as the number of connected devices continues to grow exponentially, even NAT's ability to extend IPv4's useful life is reaching its limits.

Technical Advantages of IPv6

Beyond the obvious benefit of a vastly larger address space, IPv6 offers several technical advantages that improve network performance, simplify administration, and enhance security.

End-to-end connectivity: Without the need for NAT, every device on an IPv6 network can have a globally unique address and communicate directly with any other device. This simplifies network architecture, improves application compatibility, and enables peer-to-peer communication that is difficult or impossible with NAT.

Simplified header format: The IPv6 packet header is actually simpler than IPv4's, despite the larger address size. IPv4 headers contain variable-length options that routers must process, while IPv6 uses a streamlined fixed-length header with optional extension headers. This allows routers to process IPv6 packets more efficiently, potentially improving throughput.

Built-in security: IPv6 was designed with IPsec as a mandatory component, providing native support for encryption and authentication at the network layer. While IPsec can also be used with IPv4, it is an optional add-on rather than an integral part of the protocol.

Stateless address auto-configuration (SLAAC): IPv6 devices can automatically configure their own addresses using information from the local router, without requiring a DHCP server. This simplifies network administration, particularly for large networks and IoT deployments.

IPv6 Adoption in the United Kingdom

The UK has made significant progress in IPv6 adoption, though it remains uneven across different sectors and providers. According to recent data, approximately 45 per cent of UK internet traffic is now carried over IPv6, placing the UK ahead of many European countries but behind leaders such as India, Germany, and France.

The adoption picture varies considerably by sector. Consumer ISPs have led the way, driven by the need to serve growing numbers of broadband subscribers without acquiring expensive additional IPv4 addresses. BT, the UK's largest broadband provider, has deployed IPv6 to approximately 85 per cent of its broadband customers. Sky Broadband has also made substantial progress. However, business-focused ISPs and hosting providers have been slower to adopt IPv6, partly because their enterprise customers have been slower to request it.

UK government digital services have been gradually adopting IPv6, with GOV.UK and several other government websites accessible over IPv6. The National Cyber Security Centre has published guidance recommending that organisations include IPv6 in their network planning, though it stops short of mandating adoption. Major UK cloud providers and data centres generally offer IPv6 connectivity, and all three major hyperscale cloud providers — AWS, Azure, and Google Cloud — fully support IPv6 in their UK regions.

What UK Businesses Should Do Now

The transition from IPv4 to IPv6 is not something that will happen overnight, and it is not something you can ignore indefinitely. The pragmatic approach for UK businesses is to adopt a dual-stack strategy — running both IPv4 and IPv6 simultaneously — that allows you to maintain compatibility with the IPv4 internet while progressively enabling IPv6 across your infrastructure.

Assess Your Current Readiness

Start by auditing your existing infrastructure for IPv6 compatibility. Most modern network equipment — routers, switches, firewalls, and wireless access points manufactured in the last five to seven years — supports IPv6. However, older equipment, particularly legacy firewalls and some managed switches, may not. Your audit should cover every network device, server operating system, and application in your environment, noting which support IPv6 natively, which require firmware updates, and which need replacing.

Check whether your internet service provider offers IPv6 connectivity on your business circuit. If they do not, request it — or factor IPv6 availability into your next ISP procurement decision. Similarly, verify that your web hosting provider, DNS provider, and email services support IPv6, and enable it where available.

Security Considerations

IPv6 introduces security considerations that many UK businesses overlook. If your network equipment supports IPv6 but you have not explicitly configured and secured it, you may have IPv6 traffic flowing on your network without any firewall rules or monitoring in place. This is a genuine security risk — attackers can potentially use IPv6 to bypass IPv4-only security controls.

Ensure your firewall policies cover both IPv4 and IPv6 traffic. If you are not ready to deploy IPv6, explicitly disable it on all network interfaces and block IPv6 at the firewall to prevent uncontrolled IPv6 traffic. When you do deploy IPv6, apply the same security principles you use for IPv4 — least privilege, defence in depth, and comprehensive logging.

The transition from IPv4 to IPv6 is a marathon, not a sprint. UK businesses that begin planning now will be well-positioned as IPv6 becomes increasingly essential for modern connectivity. Those that delay will face rising IPv4 costs, compatibility challenges with IPv6-native services, and a more expensive and disruptive transition when they are eventually forced to act.