How to force NTP in Debian/Ubuntu to synchronize to IPv4 servers, not IPv6 (default \w both proto)

How to force NTP in Debian/Ubuntu to synchronize to IPv4 servers, not IPv6 (default \w both proto)

After enabling IPv6 in the network, NTP daemon uses ipv6 DNS resolution to synchronize to ntp servers:

Code:

# ntpq -pn
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 2001:b31:5c02:1 .INIT.          16 u    -   64    0    0.000    0.000   0.000
 2001:b31:5c02:1 .INIT.          16 u    -   64    0    0.000    0.000   0.000

If this is not required, edit the "/etc/default/ntp" file and add the "-4" startup option for ntpd so that it uses IPv4 dns resolution.

From "man ntpd":

Quote:

OPTIONS
-4, --ipv4 Force IPv4 DNS name resolution. This option must not appear
in combination with any of the following options: ipv6.

Force DNS resolution of following host names on the command
line to the IPv4 namespace.

-6, --ipv6 Force IPv6 DNS name resolution. This option must not appear
in combination with any of the following options: ipv4.

Force DNS resolution of following host names on the command
line to the IPv6 namespace.