Running IPv4 and IPv6 Together

IPv4 and IPv6 are not directly compatible, so the internet cannot switch overnight. Instead, both run side by side for years during the transition.

Network professionals must support both, which is why the Network+ exam covers the techniques that let the two versions work together smoothly.

The most common approach is dual-stack, where a device runs both IPv4 and IPv6 at the same time. It holds an address of each type and chooses which to use per destination.

Dual-stack is the preferred transition method because it requires no translation — each protocol simply uses its own native path.

On a dual-stack host, the operating system generally prefers IPv6 when both a destination and the path support it, falling back to IPv4 otherwise.

This choice is guided by the DNS records returned: an AAAA record points to IPv6, an A record to IPv4. The device picks based on what is available and reachable.

When a native path for one protocol is missing, tunneling wraps one protocol inside the other. For example, IPv6 packets can be encapsulated inside IPv4 to cross an IPv4-only segment.

Tunneling mechanisms let isolated IPv6 islands communicate across an IPv4 internet until native IPv6 is available end to end.

NAT64 translates between IPv6 and IPv4, letting an IPv6-only client reach an IPv4-only server. It works with DNS64, which synthesizes the needed AAAA records.

Translation is more complex than dual-stack and is used when one side cannot speak the other protocol at all, such as modern IPv6-only mobile networks reaching legacy services.

DNS bridges the two worlds through record types. An A record maps a name to an IPv4 address; an AAAA record maps a name to an IPv6 address.

A dual-stack server publishes both, so each client receives the address matching its capabilities. Correct DNS records are essential for smooth dual-stack operation.

Choose the method based on what each end supports:

• Both support both → dual-stack (simplest).
• IPv6 islands across IPv4 → tunneling.
• IPv6-only to IPv4-only → translation (NAT64/DNS64).

Dual-stack is favored wherever possible because it avoids translation overhead.

Dual-stack adds troubleshooting nuance. A name may resolve over IPv6 but the IPv6 path is broken, causing slow or failed connections even though IPv4 works.

Tools like ping and traceroute have IPv6 modes (ping -6) so you can test each protocol independently and pinpoint which stack has the fault.

Vast numbers of services, devices, and networks still run only IPv4. Turning it off would break access to large parts of the internet, so IPv4 remains essential.

The transition is gradual by necessity. Expect to support both protocols throughout your career, even as IPv6 adoption steadily grows.

In practice, most modern networks are dual-stack: clients, servers, and routers all carry IPv4 and IPv6 addresses. Mobile carriers increasingly run IPv6-only cores with NAT64 to reach legacy IPv4 services.

Understanding which mechanism is in play helps you diagnose connectivity issues and design networks that work for everyone.

The key takeaway: IPv4 and IPv6 coexist, with dual-stack as the default, tunneling for crossing incompatible segments, and translation for one-protocol-only endpoints.

You have now completed the IPv6 essentials and can read, classify, and integrate IPv6 alongside the IPv4 you already know.

Pick the transition method.

You learned to run IPv4 and IPv6 together.

• The two are not compatible, so they coexist during a long transition.
• Dual-stack runs both natively and is preferred.
• Tunneling wraps one protocol inside the other across incompatible segments.
• NAT64/DNS64 translates between IPv6-only and IPv4-only ends.
• DNS uses A (IPv4) and AAAA (IPv6) records to guide selection.