I recently installed a Netvanta 3140 router to provide Internet and VPN connectivity. I also configured the Netvanta 3140 to secure time via NTP from tine.nist.gov.
ntp server time.nist.gov
For reporting and logging consistency, other switches (Netvanta 1534, 1544, etc.) on the network should be time synced with the router. PCs also should sync time from a known source. PCs require NTP.
I struggled with the fact that the Netvanta 3140 will support NTP or SNTP but not both at the same time.
I discovered that I could request SNTP time service from the other switches on the network by pointing them to the LAN side of the Netvanta 3140.
sntp server 10.10.10.2
Even though sntp server is not enabled on the Netvanta 3140, it satisfies those requests.
The only other issue that I encountered is that DNS returns a IPV6 address for time.nost.gov. My router is assigned an IPV4 public IP address but does not have an IPV6 address on its WAN interface. This prevents it from communicating with time.nist.gov. At Adtran's suggestion, I made a static host entry and assigned the V4 address.