[j-nsp] Windows NTP server for JUNOS client

[Jared Gull]

Hi Abdullah,

I have seen others experience issues when using a Windows server as their NTP server when that server does not have an external time source. Does your Windows NTP server have an upstream time source? If not, you could try to link it with one to see if that fixes the issue. If not, you may need to do some local modifications on the server. As I understand it the issue stems from a high root dispersion value on the WIndows server. You can confirm the root dispersion value by capturing an inbound NTP packet on your Junos device: 
 
12:40:22.325750  In 
        Juniper
PCAP Flags [Ext, no-L2, In], PCAP Extension(s) total length 22
         
Device Media Type Extension TLV #3, length 1, value: Ethernet (1)
         
Logical Interface Encapsulation Extension TLV #6, length 1, value: Ethernet
(14)
         
Device Interface Index Extension TLV #1, length 2, value: 132
         
Logical Interface Index Extension TLV #4, length 4, value: 365
         
Logical Unit Number Extension TLV #5, length 4, value: 511
       
-----original packet-----
       
PFE proto 2 (ipv4): (tos 0x0, ttl 126, id 28940, offset 0, flags [none], proto:
UDP (17), length: 76) 10.11.14.1.123 > 10.13.11.248.123: [udp sum ok] NTPv3,
length 48
       
Server, Leap indicator:  (0), Stratum 3, poll 9s, precision -6
      
 Root Delay: 0.000000, Root
dispersion: 10.062759, Reference-ID: 202.175.115.244
         
Reference Timestamp:  3572566348.629499999
         
Originator Timestamp: 3572570422.323693987
         
Receive Timestamp:    3572570422.316499999
         
Transmit Timestamp:   3572570422.316499999
           
Originator - Receive Timestamp:  -0.007193988
           
Originator - Transmit Timestamp: -0.007193988
 
If you see the high root
dispersion and you are using Windows 2003/2008 server, you can change the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\W32Time\Config\LocalClockDispersion from value 10 to value 0 and then restart the time
services in the command prompt by “w32tm /config /update”. After that you can then
capture the NTP packet again the see that the value has changed and verify the client no synchronizes with the server.

Hope this helps,

Jared



________________________________
 From: Abdullah Baheer <abdullahbaheer at yahoo.com>
To: "juniper-nsp at puck.nether.net" <juniper-nsp at puck.nether.net> 
Sent: Wednesday, July 24, 2013 6:13 AM
Subject: [j-nsp] Windows NTP server for JUNOS client
 

Hi

Has anyone tried to synchronize NTP from Junos device towards Windows NTP server (NTP running as a service from Windows)?
I am trying and getting the following output:
show ntp associations 
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 192.168.x.x  .LOCL.           1 -    1   64    1    3.438  -13033.  73.051

There is no "*" in the beginning, in stead there is a space, which I checked and it means:
    * space—Discarded because of a high stratum value or failed sanity checks.
My Netscreen devices are able to sync with this NTP server.

Thanks
Abdullah Baheer
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