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Community Member

Problem with NTPv4 over IPv6

Dear All,

When I was doing PoC for IPv6 transition, I had to work with NTPv4 for native IPv6. I am using 3825 running 12.4(24)T  adv enterprise.

As per Cisco documents NTPv4 is supported in 2 modes.

1. Client - Server.

2. Multicast.

I am presently interested in Client Server Mode

In this mode I configured Server with command. 'ntp master 2'

And on the client I configured:


ntp update-calendar

ntp server FD00:0:0:60::1 source Loopback0


Loopbacks of both server and client are reachable using OSPF.

But NTP remains unsynchronised forever.

Are there any known issues with NTPv4 over native IPv6 ?

Everyone's tags (2)
Community Member

Problem with NTPv4 over IPv6

Hello Maulik,

I am running a 1921 in a production environment and the NTP config includes:

ntp update-calendar

ntp peer

ntp peer

ntp peer

ntp server

ntp server 2001:67C:288::128

(the router is running dual stack)

sh ntp associations


  address         ref clock       st   when   poll reach  delay  offset   disp

+~    2    710   1024   377  2.047   0.721 15.742

~   .STEP.          16      -   1024     0  0.000   0.000 15937.

~    4    862   1024   377  2.006  -1.532 19.759

~  .STEP.          16      -   1024     0  0.000   0.000 15937.


           2    703   1024   377 97.275   5.325 14.800

* sys.peer, # selected, + candidate, - outlyer, x falseticker, ~ configured

So apparently NTP works over native IPv6. I suppose connectivity (including access lists) is verified between the two devices .... try debug ntp packet and events.



Community Member

Problem with NTPv4 over IPv6

HI fabios,

Thanks for your reply.

I was able to synchronize NTP when running dual stack. It was just that when i used native IPv6, it didn't work.

Not a single ACL configured.

Strange thing is that when i use IPv6 on server, (i.e. Master) it gets reference clock as some public IPv4 address and says synchronised, whereas I never configured that.

Unfortunaltely we have dismanteled tht setup. If i get a chance again, I will surely post the configs.



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