IPv6 in 2025 – Transitioning to IPv6

November 3, 2025

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The third in a collection of blogs all through 2025 highlighting the state of IPv6 throughout the business, finest practices to contemplate, and the way Cisco helps clients on their journeys with its services and products.

The IPv6 transition has been underway for practically 30 years, with IPv6 visitors on the Web now surpassing 50% by all measures [1]. Most functions and community stacks now favor IPv6 by default, and because of applied sciences like Completely satisfied Eyeballs [2], finish customers in a dual-stack setting hardly ever discover if IPv6 fails over to IPv4. Happily, that failure situation is turning into much less frequent because the robustness of the IPv6 Web improves and end-user networks are deployed with nice confidence.

Two Broad Phases

The journey to IPv6 usually happens in two broad levels: first, by shifting from IPv4-only to a dual-stack world, the place we activate IPv6 and run each protocols concurrently; after which progressively retiring IPv4. Conventional dual-stack deployments are sometimes accomplished in what is usually known as the “Inside Out” technique, the place the core of the community shall be dual-stacked first. As soon as routing and operational expertise are established within the community infrastructure and every part else is in place (see beneath), edge entry switches and APs will lastly allow IPv6 on their user-facing segments, offering end-users with IPv6 connectivity. Later, the transition from dual-stack to IPv6-only happens in roughly the reverse order.

Web Edge and Information Facilities

Earlier than we will dual-stack our customers, we should dual-stack our Web Edge with help from our safety group (who must be concerned from the beginning!). As soon as the Web Edge helps IPv6, focus shifts to the Information Facilities; dual-stacking the servers permits us to start verifying software entry over IPv6 whereas most customers proceed to make the most of IPv4 (with particular take a look at customers being dual-stacked). The community group and assist desk must be dual-stacked to allow them to begin experiencing the transition firsthand. (On a associated observe, ultimately all management-plane capabilities of community operations can transfer to IPv6-only whereas the data-plane stays dual-stacked). Subsequent the DMZ will be transitioned and DNS entries offered to construct an Web presence with IPv6. And eventually, IPv6 will be deployed to user-facing VLANs.

NetFlow and Site visitors Monitoring

Ideally, 100% of our inner functions shall be IPv6 enabled and most well-liked. NetFlow assortment of inner visitors helps monitor this, shortly figuring out legacy functions for remediation (by way of upgrades, replacements, or front-ending with dual-stacked units). The objective is for the one remaining IPv4 visitors on the community to be certain to the Web. NetFlow ought to present that Web-bound IPv6 visitors is steadily growing as different organizations full their personal IPv6 transition.

DNS64 and NAT64

As soon as the dual-stack transition is full and any brokenness hidden by Completely satisfied Eyeballs has been proactively recognized and stuck, it’s time to incrementally take away IPv4 from the community. Happily, the requirements our bodies have outlined NAT64 [3] and DNS64 [4] for simply this use case. These complementary applied sciences enable an IPv6-only shopper to achieve IPv4-only content material, allowing the usage of IPv6 as the only protocol throughout the community [5]. Whereas DNS64 and NAT64 could also be deployed earlier than totally eradicating IPv4 to realize familiarity and expertise, the true magic occurs as soon as IPv4 is gone.

IPv6-mostly and CLAT

With dual-stack and NAT64 in place, the subsequent step is shifting to an IPv6-mostly deployment, a brand new paradigm constructed on a set of applied sciences [6][7] that gives a better glide path to an IPv6-only future. In IPv6-mostly, the shopper working system supplies its personal IPv4-to-IPv6 translator referred to as a CLAT (customer-side translator) for functions that also have IPv4 dependencies. Whether or not the vacation spot is IPv4-only or the applying code makes use of embedded IPv4 literals, this visitors is translated into IPv6 packets throughout the IPv6-only enterprise community, after which again to IPv4 on the edge by way of NAT64. Shoppers are signaled to make the most of IPv6-mostly on dual-stack entry segments by way of DHCP Possibility 108, a DHCPv4 possibility that tells the shopper it’s secure to forgo an IPv4 deal with and run solely IPv6. As a result of IPv4 remains to be being provided, an IPv6-mostly community continues to service purchasers that don’t help native translation by way of CLAT. Now purchasers can select the protocol to make use of based mostly on their capabilities, fairly than being pressured by the community.

IPv6-only Future

As we proceed to observe community visitors with NetFlow, we must always count on to see IPv6 visitors proceed to steadily improve and ultimately we validate there isn’t any longer any utilization of IPv4 on sure consumer VLANs. That’s the time to take away IPv4 from these community segments. As extra IPv4 is turned off, it may also be faraway from the community infrastructure tools. At some point, within the hopefully not-to-distant future, 100% IPv6 utilization shall be seen on the Web Edge and within the DMZ. Till then, NAT64, DNS64 and CLAT will proceed to serve us properly.