It sounds like you're encountering a known issue related to how iOS handles captive portals, particularly when websites are only accessible via IPv4. Apple has been aware of certain behaviors where iOS might prioritize IPv6 over IPv4, leading to incomplete captive portal experiences if the necessary IPv4 infrastructure isn't present. Here are a few points and potential workarounds you might consider:
Understanding the Behavior:
iOS is designed to prefer IPv6 when both are available because it's generally faster and more efficient. However, this can cause issues on networks that only support IPv4 for certain services, like captive portal pages.
iOS and iPadOS Versions:
Apple has made various improvements to captive portal handling across different iOS versions. While I don't have specific details on version 36.2, issues related to IPv6 preference have been addressed in updates prior to and possibly after this version. Ensuring your devices are running the latest compatible version of iOS/iPadOS is always a good practice.
Network Configuration:
Dual-Stack Configuration: Ensure your network is configured to support Dual-Stack IPv4/IPv6. This setup allows devices to use IPv6 when available but fall back to IPv4 when necessary.
Force IPv4 for Captive Portals: Some network equipment allows you to enforce IPv4-only access for captive portal pages. This can be a workaround if your network supports such a configuration.
Mitigation Strategies:
Manual IPv4 Force: On affected devices, you can try forcing an IPv4 connection by disabling Wi-Fi, turning on Airplane Mode, re-enabling Wi-Fi, and then connecting to the network. This sometimes resets the network stack to prioritize IPv4.
Alternative DNS Servers: Consider using DNS servers that prioritize IPv4 responses. Public DNS services like Google DNS (8.8.8.8, 8.8.4.4) or Cloudflare DNS (1.1.1.1) can sometimes help mitigate this issue.
Apple Feedback:
If this issue persists and significantly impacts your users, consider providing feedback to Apple through the Developer Feedback Assistant. Detailed logs and descriptions of the environment can help Apple diagnose and address the problem in future updates.
