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New Member

Combining SNTP and NTP


I am trying to setup the follow scenario.

I have several devices running the protocol NTP. I also have 1 cisco router 1751 (IOS ver 12.2<15>T13) and 1 cisco router 3745 (IOS ver 12.3<8>T). Furthermore all of these devices are in a network with several windows 2008 domain controllers.

Since it is not possible to sync a device running NTP to a windows domain controller as the domain controller is running SNTP and not NTP, I would like to sync the 1751 router to the domain controller using SNTP and then enable the router as an NTP server so that other devices can sync to the router using NTP. In order to do this I use the commands :



Then I execute the following commands(with there output) to confirm that the router is in sync

router#sh sntp

SNTP server Stratum Version Last Receive 2 1 00:00:55 Synced

router#sh ntp asso

address ref clock st when poll reach delay offset disp

*~ 2 32 64 377 0.0 0.00 0.0

* master (synced), # master (unsynced), + selected, - candidate, ~ configured

In order for the 3745 router to sync with the router 1751 I use the following commands on the router 3745:

NTP SERVER (IP of the 1751 router)

But for some reason the router does is not able to contact the NTP server or better say the NTP server does not respond to the NTP request from the client. I know that there is connectivity between the two routers as they are able to ping each other. Also not that there is not firewall between the devices.

The following command on the 3745 router shows that it is not getting a response from the router 1751:

VALENTINE#sh ntp asso

address ref clock st when poll reach delay offset disp

~ 16 - 64 0 0.0 0.00 16000.

* master (synced), # master (unsynced), + selected, - candidate, ~ configured

I have a feeling that combination of the SNTP and the NTP commands in the router 1751 that I configured in the routers is not suppported, but I cannot find any documentation that confirmed this.

Can you help me determining the case of my problem? Is there another solution to sync a Cisco device to a windows domain controller?



New Member

Re: Combining SNTP and NTP

I have my core switches NTP to Windows DC and it is working fine.

I've followed the Microsoft guide to implement SNTP but i whack in the NTP configs and they work fine.

Perhaps you can try that and see if it can sync via NTP first.

I dont see any reason why SNTP client and NTP master cannot exist in the same device.

New Member

Re: Combining SNTP and NTP

Did you make any special config to your DC? beside pointing your switches to your DC did you config anything else to get it working.

If possible can you give me the link to the resources you used.

New Member

Re: Combining SNTP and NTP


Follow the guide and you'll have your NTP server up in no time.


Hall of Fame Super Silver

Re: Combining SNTP and NTP

This is a very interesting and helpful response. I am guessing that you followed the steps to make the Windows server have an authoritative time source. And I am guessing that Screech did not do this.

In IOS if a router has learned authoritative time then it is enabled to send time to other devices. I believe that learning time from SNTP does not qualify as authoritative time. If Screech follows the steps so that the server is providing authoritative time then I believe that his router will function to offer time to other network devices.