Using windows 2003 as a NTP server to Cisco and HP devices

[Matt Hobbs · Accepted solution]

I tried again today with a 2003 server that was only part of a workgroup. Initially it would not respond to any NTP requests, so I went into the registry and in the key:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\NtpServer

I changed Enabled from 0 to 1.

It would now respond but the Cisco 2600 would not accept the time - I initially though it was because it was given either due to it being an unspecified stratum, or it having a null reference clock ID.

I went to apply the "Configuring the Windows Time service to use an internal hardware clock" but it looks to be that way by default on non-domain controllers.

Finally I applied the external time clock method, this still didn't work! Closer inspection in the packet capture revealed the only difference being the 'clock dispersion' was 16 seconds. My other one was under a second. I can see on your traces that it was around 10 seconds.

Next I simply rebooted this server, it still didn't work immediately as it hadn't synced to the external time source. Once it synced though, it's 'clock dispersion' was now under a second and then the sync to the Cisco worked fine.

My theory now is that some devices required the 'clock dispersion' to be under 1 second.

[Matt Hobbs]

Since yours was at 10 seconds, try changing it to 1 maybe:

http://technet2.microsoft.com/WindowsServer/en/library/a9fb3bdd-766e-4137-9321-d9dc14a08b0d1033.mspx?mfr=true

[Ashly A K]

mm...i too did little reading for you, please see the below stuffs :

Windows 2000 uses SNTP while Windows 2003 use NTP. I belive, Cisco Devices above 1600 routers all use NTP and a NTP client cannot sync to a SNTP Server

See the below link :
http://www.microsoft.com/technet/prodtechnol/windowsserver2003/technologies/security/ws03mngd/26_s3wts.mspx
http://www.tek-tips.com/viewthread.cfm?qid=1310139&page=4

-Ashly

[Hugo Tigre]

Matt:

right on the money.. :)

I changed LocalClockDispersion to 0, and it finally worked with NTP.

Now i just need to check if this has any implication to windows xp clients and current sntp client devices. And i need to test this with different IOS versions.

But finally a breakthrough :)

I attached the new sniffed packets if anyone wants to see the clock dispersion value.

i will post any new developments in this matter.

best regards,
hugo

[Hugo Tigre]

ups... forgot to attach the file