[ntp:questions] Ntpd and changing IP addresses

Danny Mayer mayer at ntp.isc.org
Wed Oct 10 11:30:04 UTC 2007

Juliusz Chroboczek wrote:
> Hi,
> I'm currently working on a project in which the set of IP addresses of
> a host changes a few times after boot.  More precisely, at any time
> a host can have
>   - a (global or NATed) IPv4 address;
>   - a global IPv6 address; or
>   - both.
> Most hosts only have IPv6 routing most of the time, and may
> occasionally have IPv4; such hosts need to have NTP work over IPv6.
> Others have IPv4 routing only before they establish a VPN to get to
> the IPv6 Internet; such hosts need to have NTP work over IPv4 (the VPN
> software requires the time to be accurate).
> Obviously, I want all the hosts to have the same NTP config, so I've
> configured two IPv4 and two IPv6 servers.  Unfortunately, if ntpd
> starts when only IPvx addresses are configured, it discards the IPvy
> servers (``couldn't find interface for xxxx'').
> Currently, I'm working around that by restarting the ntp daemon
> whenever the set of IP addresses changes.  Is there a way to tickle
> the ntp daemon so that it notices that the set of IP addresses has
> changed?  Even better, is it possible to have ntpd daemon deal
> automatically with address changes?

What version of ntpd are you running? The stable release 4.2.4 supports
dynamic address changes of the interfaces. I believe that the default
check interval is currently every 10 minutes but can be changed on the
command line.


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