Net time

Hi,

I have a domain with 2 DC on one site. The third DC is
locate on a remote site through a vpn connection. The
problem is the net time is configured on both sides to
bring time to the clients. But curiously both DC'S from
the first site try to update their time with the third DC
on the remote site

Why is happens that? If them should synch themselves and
the clients on their site.

-So, if the VPN going down by any reason the network crash
over the time synch.

What may i do to set the net time on both sites availables
without matter if the VPN is up or down !!!

Thanks any advance