Now, if I force ntpd to use only ipv4 DNS with the -4 option, everything works fine

But I don't want to do this because if I go to a network that only gives ipv6 addresses this will fail. Is there a way to configure ntp to only use ipv4 ( or ipv6 ) if my interface actually has an ip address in that family?

I have figured out the root cause of why this started to happen. I recently disabled ipv6 forwarding on my system. Once I turn ipv6 forwarding back on, ntp starts using the ipv4 address as I would expect.

By default the system boots with ipv6 forwarding disabled. To turn it on, in one of the boot scripts I have the line:

Now, if I force ntpd to use only IPv4 DNS with the -4 option, everything works fine

But I don't want to do this because if I go to a network that only gives IPv6 addresses this will fail. Is there a way to configure NTP to only use IPv4 ( or IPv6 ) if my interface actually has an IP address in that family?

I have figured out the root cause of why this started to happen. I recently disabled IPv6 forwarding on my system. Once I turn IPv6 forwarding back on, NTP starts using the IPv4 address as I would expect.

By default the system boots with IPv6 forwarding disabled. To turn it on, in one of the boot scripts I have the line:

By default the system boots with ipv6 forwarding disabled. To turn it on, in one of the boot scripts I have the line:

sysctl -w net.ipv6.conf.all.forwarding=1

The version of ntpd is 4.2.8p12. This is the ntp.conf file:

tinker panic 0                                                              
                                                            
driftfile /usr/local/etc/ntp.drift                                          
disable auth                                                                   
                                                                         
# Update the realtime clock and override its default                         
# stratum of 0.                                                                   
server time.google.com prefer #Real Time Clock                             
server 127.127.1.0 #Real Time Clock                           
server 127.127.1.0 #Real Time Clock                                         
fudge 127.127.1.0 stratum 10                                      
broadcast ff0e::101 iburst ttl 7              

I have figured out the root cause of why this started to happen. I recently disabled ipv6 forwarding on my system. Once I turn ipv6 forwarding back on, ntp starts using the ipv4 address as I would expect.

Why would turning on ipv6 forwarding do this?