# IPv6-only DNS64 NAT64 review network and IPv4-literal probes and Guideline 2.5.5 and Internet Sharing NAT64 testing > Source-anchored research for IPv6-only DNS64 NAT64 review network and IPv4-literal probes and Guideline 2.5.5 and Internet Sharing NAT64 testing. Run status: COMPLETED. Parent: [Mac App Store Readiness: Residual Gaps for Sandboxed Monitors](https://llms-explorer.com/tree/mac-appstore-readiness-residual-gaps/) · 5 facets · 8 facts · page: https://llms-explorer.com/tree/ipv6-only-dns64-nat64-review-network-and-ipv4-literal-probes-and-guideline-2-5-5-and-internet-sharing-nat64-testing/ ## How it works - RFC 8880 defines ipv4only.arpa (A: 192.0.0.170, 192.0.0.171) for NAT64 prefix discovery; a DNS64 resolver synthesizes AAAA records from the local prefix. Queries must go to the interface's own advertised resolver, not user-configured, VPN or local resolvers, because the NAT64 prefix is per-interface. (medium confidence) — [source](https://www.rfc-editor.org/rfc/rfc8880.html) ## How-to and procedures - To reach an IPv4-literal-only target on a NAT64 network, pass the literal string to getaddrinfo with AF_UNSPEC (AI_DEFAULT); on OS X 10.11.2+/iOS 9.2+ it synthesizes an address such as 64:ff9b::192.0.2.1. Apple warns against synthesizing the Well-Known Prefix address manually. (high confidence) — [source](https://developer.apple.com/library/archive/documentation/NetworkingInternetWeb/Conceptual/NetworkingOverview/UnderstandingandPreparingfortheIPv6Transition/UnderstandingandPreparingfortheIPv6Transition.html) ## Problems, failure modes and limitations - Apple's recommended app-side checks: dig AAAA for each server; an IPv4-mapped ::ffff:x.x.x.x in AAAA is invalid; a crash or failure on the review network is treated as an app bug, not a network problem. (low confidence) — [source](https://developer.apple.com/forums/thread/49979) ## Comparisons and alternatives - Apple lists these as common IPv4-literal failures on DNS64/NAT64: IP literals in protocols and config files, network preflighting with 0.0.0.0 or 169.254.0.0, and IPv4-only low-level APIs (gethostbyname, inet_aton, inet_addr, inet_ntoa) and storage (in_addr, sockaddr_in rather than sockaddr_storage). (high confidence) — [source](https://developer.apple.com/library/archive/documentation/NetworkingInternetWeb/Conceptual/NetworkingOverview/UnderstandingandPreparingfortheIPv6Transition/UnderstandingandPreparingfortheIPv6Transition.html) ## Facts and statements - App Review Guideline 2.5.5 states apps must be fully functional on IPv6-only networks; Apple's IPv6 page says support has been required for all App Store submissions since June 1, 2016. (high confidence) — [source](https://developer.apple.com/support/ipv6) - Reachability guidance: do not use SCNetworkReachabilityCreateWithAddress with 0.0.0.0; use SCNetworkReachabilityCreateWithName with a hostname instead. (medium confidence) — [source](https://developer.apple.com/library/archive/documentation/NetworkingInternetWeb/Conceptual/NetworkingOverview/UnderstandingandPreparingfortheIPv6Transition/UnderstandingandPreparingfortheIPv6Transition.html) - Local NAT64 test network: connect the Mac to the Internet by a non-Wi-Fi link, Option-click Sharing, choose Internet Sharing, tick Create NAT64 Network, configure Wi-Fi Options, then enable Internet Sharing. On the client, disable other interfaces (cellular/other Wi-Fi) so only the NAT64 network is used. (high confidence) — [source](https://developer.apple.com/library/archive/documentation/NetworkingInternetWeb/Conceptual/NetworkingOverview/UnderstandingandPreparingfortheIPv6Transition/UnderstandingandPreparingfortheIPv6Transition.html) - Apple DTS says the App Review NAT64 network (ARNAT64) now behaves like the Mac Internet Sharing NAT64 (MacNAT64): it always synthesizes IPv6 addresses and lacks direct IPv6-to-IPv6 egress. So MacNAT64 is a close local proxy for review, though not identical. (medium confidence) (verified as of 2017-09-27) — [source](https://developer.apple.com/forums/thread/49979)