# App works on IPv6-only networks

- **Pattern:** `ab-000504` (`app-store-review-blockers.technical-requirements.ipv6-compatible`)
- **Severity:** medium
- **Lifecycle:** active
- **Last modified:** 2026-04-18
- **Canonical URL:** https://auditbuffet.com/patterns/ab-000504
- **License:** CC-BY-4.0 — attribute to AuditBuffet Pattern Catalog (https://auditbuffet.com/patterns/ab-000504)

## Why it matters

Apple requires all iOS apps to work on IPv6-only networks and tests this during review using an IPv6 NAT64 hotspot. Hardcoded IPv4 addresses (e.g., `192.168.1.100` that leaked from a development config) break immediately on IPv6-only networks because those addresses cannot be reached. This is a direct rejection cause for iOS submissions. ISO 25010:2011 operational-readiness requires software to function in the range of environments it claims to support — IPv6-only networks are widespread in cellular carrier environments and Apple's own review lab.

## Severity rationale

Medium because IPv6 failures cause rejection only during Apple's specific IPv6 test, but that test reliably catches any hardcoded IPv4 production URL.

## Remediation

Replace every hardcoded IPv4 address in production configuration with a hostname.

```ts
// src/config/api.ts
// Wrong — fails on IPv6-only networks:
export const API_URL = 'http://192.168.1.100:3000';

// Correct — DNS resolves to IPv4 or IPv6 as needed:
export const API_URL = process.env.EXPO_PUBLIC_API_URL ?? 'https://api.yourdomain.com';
```

To test IPv6 compatibility on macOS: go to System Settings > Sharing > Internet Sharing, share your Ethernet connection over Wi-Fi, enable "Enable IPv6" in the Wi-Fi options. Connect your test device to this hotspot and run the app. Any hardcoded IPv4 URL will fail immediately.

## Detection

- **ID:** `ipv6-compatible`
- **Severity:** `medium`
- **What to look for:** Count all relevant instances and enumerate each. Search for hardcoded IPv4 addresses in source files: patterns like `\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}` in API base URLs, server configuration, or network code. Look for `getaddrinfo` calls with `AF_INET` only (IPv4), socket creation with `AF_INET` that excludes `AF_INET6`, or any hardcoded IP literals in network configuration. In React Native, check `app.json`, `.env` files (for local development IPs that may have leaked into production config), and any `fetch()` base URLs. Also look for third-party libraries with known IPv6 issues — check the library's issues tracker if you find unusual networking code.
- **Pass criteria:** No hardcoded IPv4 addresses in production API URLs. At least 1 implementation must be verified. All network connections use hostnames (which DNS resolves to IPv4 or IPv6 as appropriate). App does not explicitly force IPv4 socket connections.
- **Fail criteria:** Hardcoded IPv4 addresses (e.g., `192.168.1.100`, `10.0.0.1`) in production API configuration; socket code that explicitly uses `AF_INET` to the exclusion of IPv6.
- **Skip (N/A) when:** App is Android-only (Google Play does not require IPv6 compatibility, though it is still good practice).
- **Detail on fail:** `"API base URL in src/config/api.ts contains hardcoded IPv4: 'http://192.168.1.5:3000'"` or `"Native iOS socket code uses AF_INET exclusively, failing on IPv6-only networks"`
- **Remediation:** Apple requires all iOS apps to work on IPv6-only networks. Apple tests this during review using an IPv6-only Wi-Fi hotspot.
  1. Replace all hardcoded IP addresses in production config with hostnames:
     - Wrong: `API_URL = 'http://192.168.1.100:3000'`
     - Correct: `API_URL = 'https://api.yourdomain.com'`
  2. Use Apple's IPv6 testing setup: create an IPv6 NAT64 hotspot via macOS Internet Sharing to test
  3. Ensure all socket code uses `getaddrinfo()` for hostname resolution (not hard-coded `AF_INET`)
  4. Third-party SDKs that use raw sockets may have IPv6 issues — check their release notes

  Review the configuration in `src/` or `app/` directory for implementation patterns.

## External references

- external apple-ipv6-requirement — https://developer.apple.com/news/techdigest/2016/06/preparing-your-app-for-ipv6-dns64-nat64-networks.html

Taxons: regulatory-conformance, operational-readiness

HTML version: https://auditbuffet.com/patterns/ab-000504