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NTP on Nexus5k and 3560

I have begun moving NTP from our 6500 to 4 Nexus 5k as part of a core upgrade.  The Nexus will act as our internal NTP server for all switches.  Any switches that are on the same vlan as the Nexus have no issues syncing NTP from them.  However any switch that has to have the traffice routed to the Nexus is showing that the time source as insane.

The configuration on our Nexus is as follows the Nexus are .11,12,13 and 14:

ntp peer

ntp peer

ntp peer

ntp server

clock timezone CST -6 0

clock summer-time CDT 2 Sun Mar 2:00 1 Sun Nov 2:00 60

Here is the configuration on one of our 3560's:

clock timezone CST -6

clock summer-time CDT recurring

ntp server

ntp server

ntp server

ntp server

This same configuration worked when the switches were configured as NTP Peers to our 6500 (  The ip for the 6500 has been moved to an HSRP address across the Nexus so I have pointed the switches at the individual IP for each Nexus.

Here is a debug ntp packet ouput from one of the 3560s:

.Mar  7 17:21:22: NTP: xmit packet to

.Mar  7 17:21:22:  leap 3, mode 3, version 3, stratum 0, ppoll 64

.Mar  7 17:21:22:  rtdel 2445 (141.678), rtdsp C804D (12501.175), refid AC180101


.Mar  7 17:21:22:  ref D2F4A4F5.9CBFA919 (06:32:53.612 CST6 Sun Feb 26 2012)

.Mar  7 17:21:22:  org 00000000.00000000 (18:00:00.000 CST6 Thu Dec 31 1899)

.Mar  7 17:21:22:  rec 00000000.00000000 (18:00:00.000 CST6 Thu Dec 31 1899)

.Mar  7 17:21:22:  xmt D3021792.8D0B8963 (11:21:22.550 CST6 Wed Mar 7 2012)

6 Replies 6

Marvin Rhoads
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VIP Community Legend

Unless you explicitly specify otherwise, Nexus's will use the Mgmt VRF for NTP. Are the remote devices routing to and from the Mgmt VRF addresses successfully?

Our Mgmt interface is not routed as we are using it for a VPC heartbeat.  I did try ntp source-interface vlan 1 and that did not fix the issue.  The odd thing I see in the debug is:

.Mar  7 17:21:22:  rtdel 2445 (141.678), rtdsp C804D (12501.175), refid AC180101 ( is the HSRP address for vlan 1.  I have ntp pointing at which is the vlan 1 interface ip on NexusA.  Just as a trial I did try changing the ntp server command to point to and that made no difference.

I did finally get this working partially.  Our MetroE cloud is layer 2.  NexusA has an interace on it of  On the MetroE end I can set I set the ntp source to the ethernet interface that has the 192.168.25. ip on it and set the ntp server it will work. 

That fixes the 3560 at each site.  However some sites have 2900's or 2950's off of the 3560.  I cannot source their ntp to come from an ip on the subnet.  I guess I could have them pull from the 3560 there.  It's not ideal but it would work.  Is this the intended behavior/setup?