Here’s a breakdown of the IPv6 settings you’re seeing on your AirPort Extreme router under the “Advanced” tab:

  • What it is: This mode uses only link-local IPv6 addresses. These addresses are automatically generated and are limited to communication within the same local network or link (e.g., devices connected to the same router or switch). They are not routable on the wider internet.
  • When to use it: Use this mode if you don’t need global IPv6 connectivity or your internet service provider (ISP) doesn’t support IPv6. This setting is useful for internal communication between devices on your local network.

2. Host Mode

  • What it is: In this mode, the AirPort Extreme acts as an IPv6 client, just like a single device. It doesn’t manage or route IPv6 traffic for other devices on the network. Instead, it only configures itself with an IPv6 address.
  • When to use it: Use Host mode when your AirPort Extreme is connected behind another router that handles all IPv6 traffic, and you don’t need the AirPort to route IPv6 traffic for other devices.

3. Tunnel Mode

  • What it is: Tunnel mode is used to encapsulate IPv6 traffic within IPv4 packets. This allows IPv6 traffic to be transmitted over an IPv4-only network. A common tunneling protocol is 6to4, which automatically creates a tunnel for IPv6 traffic without requiring specific configuration on your ISP’s end.
  • When to use it: Use Tunnel mode if your ISP does not natively support IPv6 but you want to access IPv6 networks. Note that this might require additional configuration and isn’t as common today since many ISPs now offer native IPv6 support.

4. Router Mode

  • What it is: In Router mode, the AirPort Extreme acts as an IPv6 router, assigning IPv6 addresses to devices on your network and routing IPv6 traffic between your devices and the internet. This mode assumes your ISP supports IPv6 and provides you with a prefix (block of IPv6 addresses) for your network.
  • When to use it: Use Router mode if your ISP supports IPv6 and you want your AirPort Extreme to manage IPv6 traffic for devices on your network. This is the most common mode when setting up IPv6 on a home router.

Choosing the Right Mode

Here’s how to decide which mode to use:

  1. If your ISP doesn’t support IPv6: Use Link-Local Only or Tunnel (if you want IPv6 tunneling).
  2. If your ISP supports IPv6 and provides a prefix: Use Router.
  3. If the AirPort Extreme isn’t your primary router: Use Host.

Let me know if you need further clarification or help setting this up!