NTP issue

[Girish_S]

Hi, 

In one of the server ntp client is not syncying with ntp server

# ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
10.195.0.252 .INIT. 16 u - 64 0 0.000 0.000 0.000
10.195.0.253 .INIT. 16 u - 64 0 0.000 0.000 0.000

Can any body help me in this issue.

P.S. This thread has been moved fromLinux>System Administration to  Linux > networking. -HP Forum Moderator

[Matti_Kurkela]

The "reach" value is 0 on both lines. It means ntpd has not received any answers from either NTP server.

Maybe something stops the queries of the NTP client from reaching the servers? Or maybe something stops the server responses from coming back to the client? Or maybe both? Or maybe the servers are configured to ignore your NTP client?

NTP uses UDP and its standard port number is 123.

Because it uses UDP, you cannot use the telnet command to verify that the port is open: telnet is a good test for TCP-based protocols only.

Are there any iptables rules in effect? Run "iptables -L -vn" to check.
Make sure UDP traffic to port 123 is allowed.

If there are any external firewalls in your network, have the firewall administrator check them too.

If the issue does not seem to be caused by a firewall/iptables configuration, then you may have to get more information.

One way would be to monitor the NTP traffic on the NTP server, to see if the query from the ntp client reaches the server or not.
This might be a good tcpdump command:

tcpdump -p -n host <NTP client IP address> and udp port 123

 (replace <NTP client IP address> with the actual IP address of the NTP client)

The "poll" column indicates how often the NTP client will attempt to access the server. As the value is currently 64 (seconds), you should let the tcpdump run for several minutes to certainly see any incoming NTP packets from the client.