Re: [lwip-devel] DNS destination address selection improvements for IPv6

[Sly Gryphon]

Hi,

Looking around some more, I have found a form on savanna.nongnu to 
request membership of the group, which I think will allow me to submit a 
patch / pull request for evaluation.

I have submitted the request. Please review and approve, so that I can 
submit a patch with my suggested implementation of RFC 6724 destination 
address selection for review.

Thanks,

Sly Gryphon


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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> lwip-devel@nongnu.org
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