[CentOS] Re: ntpd stuck on stratum 16 = not synced
Sean Carolan
scarolan at gmail.com
Wed Jan 16 17:38:07 UTC 2008
> The zeros in the "reach" column indicate that the server has been unable to
> receive any packets from the upstream servers.
>
> Is your server inside a firewall? If so, perhaps it is blocking NTP traffic.
> You need to have it allow UDP port 123 in both directions. You don't need
> port forwarding from outside to in, since all incoming packets will be replies
> to outgoing packets.
>
> If it is not inside a firewall, perhaps you have iptables on the server itself
> blocking UDP port 123 traffic.
Fantastic, Tony. This is the information I needed. Our ISP does in fact
block UDP packets and I suspect this is why the sync is failing.
One question though - how come I can use ntpdate servername to update them by
hand? Shouldn't that be blocked as well?
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