What IPv6 is

IPv6 (Internet Protocol version 6) is the network-layer protocol that assigns IP addresses and enables devices to reach each other over the Internet and local networks. Its main motivation is address space: IPv6 uses 128-bit addresses, which provides vastly more combinations than IPv4’s 32-bit addresses.

An IPv6 address is typically written in hexadecimal and organized into groups separated by colons. Beyond the full address format, the important idea is that IPv6 supports different address types for different purposes (for example, addresses meant for local links versus globally reachable addresses).

How IPv6 works (plain-language overview)

In a basic home or office network, IPv6 typically follows this flow:

  • Devices obtain an IPv6 address, commonly via Router Advertisements (RA) and/or DHCPv6.
  • When a device needs to talk to another device on the same local network, it performs address-to-link resolution using Neighbor Discovery (ND).
  • For communication across networks (e.g., the wider Internet), routers forward packets based on routing tables.
  • DNS still plays a central role: most people use hostnames, and DNS maps those names to IPv6 addresses.

For local discovery and communication setup, IPv6 often uses multicast rather than broadcast. That affects how network equipment behaves and how firewall policies should be written.

Differences and limits compared with IPv4

Even though IPv6 is designed as a successor, it doesn’t automatically remove all IPv4-related complexity.

First, IPv6 and IPv4 are different protocols. A client on IPv6-only may not reach an IPv4-only service unless the network uses translation mechanisms (for example, dual-stack deployments where both protocols are available, or specific tunneling/translation approaches). Whether a given path works depends on the actual network configuration.

Second, common “it should work” assumptions can fail:

  • DNS answers might not include an AAAA record (IPv6 address) for a hostname.
  • Firewalls may allow IPv4 but block IPv6 traffic.
  • Router or host configuration issues (like missing default routes) can prevent connectivity.

Third, the move away from NAT in many IPv6 setups changes how troubleshooting looks. IPv6 connectivity issues aren’t always “fixed” by the same methods used for IPv4.

Finally, your ISP and your local network equipment must both support the IPv6 mode you’re using. If parts of the path don’t support IPv6, connections can fail even when the local device is configured correctly.

Practical checks you can do

Use a small set of targeted checks to confirm IPv6 is actually working end-to-end:

  1. Confirm IPv6 configuration on the device. Check whether your operating system has an IPv6 address assigned and whether a default route is present.
  2. Verify DNS returns IPv6. For a hostname you expect to reach, check that DNS provides an IPv6 address (often via an AAAA record), not only an IPv4 address.
  3. Test local reachability. Ensure you can reach the local gateway/router over IPv6 and that link-local communication is functioning.
  4. Test external connectivity. If you can, try reaching an IPv6-capable destination and observe whether the failure is immediate (configuration/firewall) or timeouts (routing/blocked path).

When troubleshooting, focus on whether the problem is inside your device, inside the local network, or beyond it in upstream routing. If IPv6 fails but IPv4 works, that strongly suggests an IPv6-specific configuration or path issue.

IPv6 is closely linked with several terms you may see in network settings and documentation:

  • Neighbor Discovery (ND): IPv6’s method for finding other devices on the local link and for link-layer resolution. If ND-related communication is blocked or misconfigured, local IPv6 may fail.
  • SLAAC: A common way for devices to form addresses from Router Advertisements. It can be used with or without DHCPv6 depending on how the network is configured.
  • Dual-stack: Running IPv4 and IPv6 at the same time. It can reduce the risk of “protocol mismatch,” but it also means troubleshooting may need to consider both protocols.

Because IPv6 behavior depends on the surrounding network (router settings, DNS, and firewall rules), outcomes can vary. If you’re unsure, check each layer—addressing, routing, DNS, and firewall—before assuming the protocol itself is broken.