[ntp:questions] Need help on NTP client

Gao gao at pztop.com
Tue Jul 28 00:13:50 UTC 2015


Hi Brian,

Thank for help.

If you read my previous email you see all these tests you recommended 
works, except this one:
   traceroute -U -p 123 $other

I think the reason is the server side don't response/echo back for UDP.

But when I running this command on the CentOS7, I also running tcpdump 
at the server end amd it DOES received lot packets on port 123:

[root at ovpn ~]# tcpdump -s0 port 123 and host 192.168.123.22
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes

17:09:40.978465 IP 192.168.123.22.54055 > ovpn.sjv.lan.ntp: NTPv0, 
unspecified, length 32
17:09:40.978495 IP 192.168.123.22.59641 > ovpn.sjv.lan.ntp: NTPv0, 
unspecified, length 32
17:09:40.978503 IP 192.168.123.22.37803 > ovpn.sjv.lan.ntp: NTPv0, 
unspecified, length 32
17:09:40.978513 IP 192.168.123.22.47468 > ovpn.sjv.lan.ntp: NTPv0, 
unspecified, length 32
17:09:40.978519 IP 192.168.123.22.39741 > ovpn.sjv.lan.ntp: NTPv0, 
unspecified, length 32
17:09:40.978525 IP 192.168.123.22.44615 > ovpn.sjv.lan.ntp: NTPv0, 
unspecified, length 32
17:09:40.978531 IP 192.168.123.22.59443 > ovpn.sjv.lan.ntp: NTPv0, 
unspecified, length 32
17:09:40.978566 IP 192.168.123.22.44037 > ovpn.sjv.lan.ntp: NTPv0, 
unspecified, length 32

I think this proves that the port 123 on server received packets from 
client. So the question is why the ntpd's NTP request to the server is 
lost somewhere, although tcpdump shows it sent out NTP request?

Gao


On 15-07-27 04:17 PM, Brian Inglis wrote:
> Hi,
> Check from each end to the other that:
>     nslookup $other
>     ping -c 5 $other
>     traceroute $other
>     traceroute -U -p 123 $other
>     ntpdate -qu $other
>     ntpdate -q $other
> all work - any failure compared to the previous result should point 
> you to the source of the problem.


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