Re: [tlug] Public NTP Servers in Japan

[Mike Gauthier <mike@example.com>]

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On 21 Dec 2002 22:24:34 +0900
Ryan Shaw <ryan.shaw@example.com> wrote:

> Hmmm...I set up my ADSL router to masquerade UDP port 123 to my 
> machine (see attached image from the router config tool), but it's 
> still not working. Is there a way to check that the router is really 
> letting things through?

Hmmm... open up a couple of terminals (xterms, console, whatever) on the ntp client machine.  In one, do a "tcpdump -nn -i <interface> port 123".  In the other, do your "ntpdate 203.139.30.195" command.  Watch the tcpdump window for ntp packets.  In this case, you should see something like this...

22:48:11.342369 192.168.0.2.123 > 203.139.30.195.123:  v4 client strat 0 poll 4 prec -6 (DF)
22:48:11.420217 203.139.30.195.123 > 192.168.0.2.123:  v4 server strat 2 poll 4 prec -18
22:48:11.420509 192.168.0.2.123 > 203.139.30.195.123:  v4 client strat 0 poll 4 prec -6 (DF)
22:48:11.497168 203.139.30.195.123 > 192.168.0.2.123:  v4 server strat 2 poll 4 prec -18
22:48:11.497328 192.168.0.2.123 > 203.139.30.195.123:  v4 client strat 0 poll 4 prec -6 (DF)
22:48:11.573991 203.139.30.195.123 > 192.168.0.2.123:  v4 server strat 2 poll 4 prec -18
22:48:11.574143 192.168.0.2.123 > 203.139.30.195.123:  v4 client strat 0 poll 4 prec -6 (DF)
22:48:11.649874 203.139.30.195.123 > 192.168.0.2.123:  v4 server strat 2 poll 4 prec -18

Notice the packets are going from you to the ntp server and then from the ntp server to you.  If you just see your packets leaving, but nothing coming back, somethings not right with your ADSL router or its rule(s).

Good luck.

- -- 
Mike Gauthier
All-purpose lackey

"Beer is proof that God loves us and wants us to be happy." - Ben Franklin


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