I have a laptop running a version of Linux ( 3.12 ). I have ntpd installed and configured to sync with time.google.com. The problem I am having is if I am plugged into a network that only provides an IPV4 address, ntp's dns is using the ipv6 address:
root@Node00b01973d6cc:~# ntpq -pn remote refid st t when poll reach delay offset jitter ============================================================================== 127.127.1.0 .LOCL. 10 l 7 64 1 0.000 0.000 0.002 ff0e::101 .MCST. 16 M - 64 0 0.000 0.000 0.002 2001:4860:4806: .INIT. 16 u - 64 0 0.000 0.000 0.000
Now, if I force ntpd to use only ipv4 DNS with the -4 option, everything works fine
root@Node00b01973d6cc:~# ntpq -pn 172.16.17.111 remote refid st t when poll reach delay offset jitter ============================================================================== 127.127.1.0 .LOCL. 10 l 60 64 1 0.000 0.000 0.002 184.108.40.206 .GOOG. 1 u 57 64 1 29.278 341.883 0.002
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?
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?
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