[ntp:questions] NTP Sync Problem

Danny Mayer mayer at ntp.isc.org
Mon Mar 5 13:27:18 UTC 2007

Ron C. wrote:
> If I set the clock to the correct time manually and then turn on the
> sync, I don't see how either the NTP server or the client can predict
> how fast the clock will drift if not adjusted.  Thus while it's true
> that 500 ppm = 43.2 sec/day, I doubt if these machines are smart
> enough to predict the future.  Yet as soon as I turn on the sync, I
> get the logged message "NTP: cannot SEND packet..." with the word
> "send" capitalized in the log.

These messages aren't from the NTP reference implementation.

> I guess I'm wondering if anyone has any idea why these relatively new
> (and otherwise flawless) routers would produce such a message in the
> first place.  Is it possibe that a received sync signal is like an
> ACK response and if it's missing the router produces the obscure
> "cannot SEND" message?  Is it possible that Covad blocks UDP port 123
> requests unless they're directed to some special non-public server?

Some firewall is blocking outgoing packets from the look of it.

> I'm having visions of all the Covad customer-premises routers all
> over the country, sending NTP requests every 3 minutes to one or the
> other of the two default servers. I've successfully sent ICMP
> requests to the servers both from my network and from the router's
> built-in ping utility.  I suspect I'm doing something wrong, just
> can't imagine what.

Contact Covad and ask them. We can't help you here except to advise you
to notify them that they need permission from the providers of NTP time
before they embed addresses in their equipment.


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