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Re: Feature request: provide ability to set a global callback function telling libcurl if IPv6 works on the system

From: Daniel Stenberg via curl-library <>
Date: Tue, 20 Sep 2022 08:22:24 +0200 (CEST)

On Mon, 19 Sep 2022, Dmitry Karpov via curl-library wrote:

> Working with IPv6-enabled dual-stack libcurl, I noticed that for some Linux
> kernel configurations, it takes ~15-30ms more for dual-stack libcurl to
> establish IPv4 connections than for IPv4 single-stack libcurl. After looking
> into this issue, it turned out that the regression was caused by
> Curl_ipv6works() function enabled in IPv6-on builds.

The origin for that IPv6 check was that back in the 90s it happened that
configure detected IPv6 support but then at runtime curl couldn't actually use

I dare to suggest that we don't see that kind of system setups and behavior
anymore. I think maybe the time has come to make instead rather assume that it
works when built IPv6 enabled. At least I think it is worth exploring that
route first before we consider adding a new API function for it.

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Received on 2022-09-20