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New Member

NTP is not synchronising

Hi, I have set up and Unix NTP server to synchronise with internet time servers and put the Unix server as ntp server on cisco boxes.

Cisco devices are in 10.20.33.0 255.255.252.0 subnet

NTP server is in 10.20.32.0 255.255.252.0 subnet

At the moment cisco boxes are not synching the time with the NTP server. However if I bring the NTP server in to the same subnet as cisco devices it is working fine. I have add both networks in the ntp.conf file

Broadcast 10.20.32.0 255.255.252.0

Broadcast 10.20.33.0 255.255.252.0

If someone can put me in the right direction to troubleshoot this I would really appreciate it.

Thanks in advance,

Anuradha.

8 REPLIES

Re: NTP is not synchronising

Can they ping each other?

New Member

Re: NTP is not synchronising

Yeah, they can ping each other. Also the ntp box is directly connected to the access switch. Same management VLAN, even then, they can not synch the NTP.

Hall of Fame Super Silver

Re: NTP is not synchronising

Anuradha

I am puzzled at the description of the problem. You say that with current addresses NTP is not syncing with the server but if you move the server into the subnet of the Cisco that they do sync. But the addresses given with the given mask are already in the same subnet (10.20.32 and 10.20.33 are in the same subnet if the mask is 255.255.252.0).

When you say that the ntp server is on the same access switch, is it in the same VLAN as the Cisco? When it works are you moving it into the same VLAN as the Cisco? If they are in the same logical IP subnet but not in the same VLAN that would be a problem that would prevent NTP sync.

HTH

Rick

New Member

Re: NTP is not synchronising

Hi Rick,

Thanks for the reply. Sorry about the confusion, I have made a mistake in my previous description.

Cisco devices were synching under following settings.

NPT subnet : 10.20.8.129 /22

Cisco Devices were on : 10.20.32.0/22 and 192.168.1.0/24

NTP was on VLAN 7,

Cisco devices management VLAN was 2.

After testing everything is working fine, I wanted to move the NTP server in to the same subnet as Cisco devices 10.20.32.0/22 and move it in to VLAN 2.

So I configured the access switch port which is connected to the NTP to be on VLAN2 and gave a static IP to the NTP server 10.20.33.150/22.

With these settings, I can ping from and to NTP server and cisco devices however devices are not synching with the NTP server. But when I move the NTP server back to 10.20.8.0/22 subnet and move back to VLAN 7 everything is working fine. So I?m pretty confident there?s nothing wrong with the NTP server end.

Thanks,

Anuradha.

Hall of Fame Super Bronze

Re: NTP is not synchronising

In a multilayer device, a packet may be sourcing from a different interface that may not be reachable by the destination.

To ensure the packet is being sourced by the correct interface, it's often recommended to have the 'ntp source [interface]' command as part of the ntp configuration.

I suggest that you deploy such feature and use the interface you pinged from the NTP server as the source.

HTH,

New Member

Re: NTP is not synchronising

I have already configured the "ntp source interface as vlan 2" (same VLAN as the NTP server). Also I tried using a extended ping using vlan 2 as the source interface and ping works.

Re: NTP is not synchronising

When the time is differing too much, you need to reload the devices to restart the synchronization process.

If everything else is OK, it will probably work after that.

regards,

Leo

New Member

Re: NTP is not synchronising

Hi Leo,

Thanks for the input, I have change the clcok settings manually, and when the NTP was on 10.20.8.x range it synchronised all my cisco devices. So time settings are up to date at the moment though it's not associating any more since I moved the NTP in to the new subnet.

Thanks,

Anuradha.

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