[Bug 270536] By default ntpd does not work on IPv6-only hosts

From: <bugzilla-noreply_at_freebsd.org>
Date: Thu, 30 Mar 2023 07:58:59 UTC 
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=270536

            Bug ID: 270536
           Summary: By default ntpd does not work on IPv6-only hosts
           Product: Base System
           Version: 13.1-RELEASE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: conf
          Assignee: bugs@FreeBSD.org
          Reporter: lapo@lapo.it

Default /etc/ntp.conf uses the following server:

pool 0.freebsd.pool.ntp.org iburst

which does not resolve to any IPv6 addresses:

% drill aaaa 0.freebsd.pool.ntp.org
;; ANSWER SECTION:

while 2 does:

% drill aaaa 2.freebsd.pool.ntp.org
;; ANSWER SECTION:
2.freebsd.pool.ntp.org. 150     IN      AAAA    2620:83:8000:ffd1:1::e
2.freebsd.pool.ntp.org. 150     IN      AAAA   
2601:603:b7f:9731:123:4636:ddb5:5de
2.freebsd.pool.ntp.org. 150     IN      AAAA    2604:a880:1:20::8e:3001
2.freebsd.pool.ntp.org. 150     IN      AAAA    2620:149:a0c:4000::1f2

I discovered about that on the following thread:

https://community.ntppool.org/t/the-time-has-come-we-must-enable-ipv6-entirely/1968/44?page=3

I'd say it would make sense to either:

1. switch entierly from 0. to 2. in order to support IPv6, but risking problems
on server which have IPv6 mis-configured
2. use both 0. and 2. in default ntp.conf, thus guaranteeing both IPv4-only
answers and IPv4+IPv6 answers, ntpd will then choose the best/closest one
anyways

cheers,
Lapo

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