DNS dynamic sort (IDFGH-12207) #65
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This fix adds an option to dynamically set the order based on whether an the host has a global (or ULA) IPv6 address, allowing a device with both IPv4 and IPv6 enabled to work in any network configuration, including IPv4-only, IPv6-only, and dual-stack. Without the option there is a static ordering preferring IPv4, which means on an IPv6-only network, a dual-stack destination returns the IPv4 address, which fails. Setting the static preference to IPv6 would have the opposite problem. A dynamic sort, based on available source addresses, is required to work on all networks.
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Working on a proper RFC 6724 implementation, but not quite ready yet; still need to do testing around different scenarios. https://github.com/sgryphon/esp-lwip/tree/sgryphon/dns-dynamic-sort-rfc6724 |
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I have tested the full RFC 6724 implementation, so dropping the PR in favour of that one: #66 |
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To address issue: espressif/esp-idf#13255
Also useful is setting up to configure the option via KConfig (a separate PR to the main esp-idf repository).
This is not a full implementation of RFC 6724 for destination address selection, but a rough approximation that checks if we have a global (or ULA) IPv6 address, and if so prioritise IPv6 first (otherwise prioritise IPv4).
The previous approach had a static preference for IPv4, which doesn't work on an IPv6-only network trying to connect to a dual-stack server.
The new option will work for all IPv4-only, IPv6-only, and dual-stack networks with standard network types (IPv4 public or private-with-NAT44, and IPv6 global addresses) and standard DNS queries (public IPv6, public IPv4). It will even work for private IPv4 and if you configure ULA and have private IPv6 to ULA addresses.