[ntp:questions] NTP Sync Problem

Ron C. nospam at nospam.com
Mon Mar 5 08:15:22 UTC 2007


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.

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?

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.

"Richard B. gilbert" <rgilbert88 at comcast.net> wrote in message news:45EB6E0D.8000604 at comcast.net...
> Ron C. wrote:
> > I'm using Netopia routers on Covad (model 4622 on T1 and 4652 on DSL).  They have built-in NTP clock syncronization with two pre-programmed servers. Although the routers work fine, I have never been able to get the sync function working. Left to themselves, they each gain 8 minutes per day so it would be nice to be able to use the sync feature.  I know that UDP port 123 should be open in both directions and as a test I turned off the firewall completely.  The device event log gives this error message "NTP: cannot SEND packet to server <ip address>" every 3 minutes, alternating between the primary and secondary NTP servers. Besides the two pre-set servers (204.152.184.72 and 18.72.0.3) I've tried several public servers from the NIST list.  BTW, I have no problem syncing computers on the same local network using a Windows-based NIST time client.  Only the router itself won't sync and gives that error message.
> 
> I don't think that there is any hope of getting those routers to 
> synchronize with NTP.  NTP generally does not cope with clock frequency 
> errors in excess of 500 parts per million or about 43 seconds per day. 
> (This is the maximum rate at which most kernels can (or will) slew the 
> system clock.)
> 
> Talk to the manufacturer about repair under warranty (if they are still 
> under warranty).  If not try a better vendor!  Cisco Systems sells top 
> quality stuff!  At top prices, of course! :-)
>




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