Thanks, Sly, Interesting work.
Definitely worth taking upstream.
Look forward to an example app.
Met vriendelijke groet / Best regards.
Teddy
I have a branch with my code from ESP-LWIP moved across. Rather than a
simple compare, I put in the structure of a full sort, and added the RFC
6724 examples as test cases.
It still takes a few short cuts and only properly handles the LWIP case
of at most 2 results (one IPv6 and one IPv4), so not all the example
will work (e.g. can't have 2x IPv6, so comparing precedence only counts
v4 vs v6).
`getaddrinfo()` now returns both results (linked; which is handled by
`freeaddrinfo()`), so you may get up to two results (e.g. could be used
for fallback/happy eyeballs in a dual stack environment).
I still need to run a test app to check it works; I couldn't see
anything in LWIP (did find some unit test though, which I used).
I will try and getting it running with my ESP-IDF setup.
Branch is here, if anyone is interested:
https://github.com/sgryphon/lwip/tree/sgryphon/dns-dynamic-sort-rfc6724
On 13/3/24 22:18, Sly Gryphon wrote:
>>> Hi,
>>>
>>> I have been working on IPv6 in ESP32 Arduino, which led back to
>>> ESP-IDF, and then some changes in ESP-LWIP.
>>>
>>> As ESP-LWIP is based on LWIP, I thought it would be best to
>>> contribute those changes upstream, as they will benefit/apply to all
>>> users of LWIP.
>>>
>>> The problem was certain specific scenarios don't work, e.g. with
>>> both protocols enabled, looking up a dual-stack server from an IPv6
>>> only network, doesn't work.
>>>
>>> The client has IPv6 enabled, the network supports IPv6, and the
>>> destination supports IPv6, but DNS lookup gives the wrong result.
>>>
>>> If you don't have IPv4 enabled, then it works fine; i.e. enabling
>>> IPv4 breaks the IPv6 scenario.
>>>
>>> An example of the problem (ESP-IDF example) is detailed here:
>>> https://github.com/espressif/esp-idf/issues/13255
>>>
>>> Ultimately it came down to the current static ordering of IPv4 vs
>>> IPv6 in LWIP DNS. (Changing the static ordering would have the same
>>> problem in reverse.)
>>>
>>> So, I have a working solution, using RFC 6724 destination address
>>> selection, which dynamically selects which destination address to
>>> use based on available source addresses. i.e. if an IPv6 global
>>> scope address (and not IPv4) is available it will return IPv6 and
>>> vice-versa. Posix/linux getaddrinfo() has a similar sorting
>>> documented (RFC 6724 replaces RFC 3484):
>>> https://man7.org/linux/man-pages/man3/getaddrinfo.3.html
>>>
>>> So rather than a static order it has dynamic ordering. I put the
>>> changes behind an option flag so that the old behaviour can be
>>> preserved. The functions are also written in such a way that we
>>> could easily add a hook to replace the default ordering if we want
>>> to add that. The current code knows you currently only get one
>>> result from DNS lookup, so maximum of 2 (one IPv6, one IPv4), so is
>>> simplified for that case, but could be extended in the future to
>>> compare multiple and keep the best (or even sort results).
>>>
>>> Note that RFC 6724 _source_ address selection is already implemented
>>> in `ip6_select_source_address()` in `ip6.c`; this code implementing
>>> destination address selection.
>>>
>>> Proposed implementation of RFC 6724 destination address selection
>>> (this is what I would like to contribute):
>>> https://github.com/espressif/esp-lwip/pull/66
>>>
>>> I am not sure how to raise a pull request against upstream LWIP.
>>>
>>> Sly Gryphon
>>>
>>>
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