Re: After enabling IPv6 curl github.com fails, succeeds with IPv4

[Mayuresh <mayuresh%warunjikar.in@localhost>]

On Wed, Jul 22, 2026 at 09:58:45AM +0530, Mayuresh wrote:
> Just wonder whether the default should be conservative i.e. do not retry
> by appending, unless a directive says so. Also wonder, how other systems
> (e.g. Linux, FreeBSD) behave in similar situation and is there any
> standard like POSIX for the resolver behavior.

Searched on this:

RFC [1] of 1993 identified this issue and the RFC is cited by the Linux
and FreeBSD documentation.

FreeBSD [2]:

    the current version of BIND that ships with FreeBSD no longer provides
    default abbreviations for non-fully qualified domain names other than
    the domain you are in. So an unqualified host mumble must either be
    found as mumble.foo.bar.edu, or it will be searched for in the root
    domain.
    ...
    Have a look at RFC 1535 for why this was considered bad practice, or
    even a security hole.


In our scenario, github.com is not a non-fqdn. So above comment doesn't
apply verbatim. But does in a broader sense of the issue.

Linux [3]:

    The default method (using RFC 1535 guidelines) follows: 
    ...
    If neither the search option in the /etc/resolv.conf file or the
    ''LOCALDOMAIN'' environment variable is used, then the search list of
    domains contains only the full domain specified by the domain option
    (in /etc/resolv.conf) or the domain used in the local hostname

[1] https://www.ietf.org/rfc/rfc1535.txt
[2] https://docs-archive.freebsd.org/doc/4.3-RELEASE/usr/share/doc/handbook/mail-trouble.html#Q18.3.1.
[3] https://linux.die.net/man/7/libbind-hostname