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Re: ai_flags in calls to getaddrinfo

From: Robin Tarsiger
Subject: Re: ai_flags in calls to getaddrinfo
Date: Fri, 1 Jan 2021 06:04:34 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0

Robin Tarsiger wrote:
> What happens if you pass nil for FAMILY but without the AI_V4MAPPED
> patch, on that system? Have you observed AI_V4MAPPED producing better
> results in any circumstance when you do not set FAMILY to ipv6?
> I conjecture that your upstream resolver is blocking AAAA queries, and
> that AF_UNSPEC is going through a slightly different path, maybe even
> issuing an ANY query which is actually responded to with records from
> both address families, which are then passed through because response
> filtering and query filtering are different. If this is close to true,
> I'm not sure there's a sane way for an application to handle
> inconsistent resolver behavior of that stripe.


Inconsistent caching resolver behavior often varies depending on the
state of the cache. So it is useful to try things like this two or
three times in a row in different orders, if you are not sure if
your DNS resolution chain is doing something dubious.


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