20 Replies Latest reply on Jan 18, 2019 4:57 AM by bcrinehart

    NTP vs SNTP, Does Anybody Really Know What Time It Is? Especially a PC

    bcrinehart Past_Featured_Member

      I've configured OpenVMS, Unix and Linux servers to request network time using NTP. On a small network where there is no server, the PCs need an accurate time source. When PCs want to know what time it is, do they look for SNTP or NTP time servers, or both?


      I configured a Netvanta 3120 to get time from nist.time.gov using NTP. It is all synced up and ready to go. There is another switch on the network, a Netvanta 1234 located in another building. I've configured a trunk between them. Both network devices have interfaces on VLAN 1. The PCs on this network connect using VLAN 10. The Netvanta 3120 has a VLAN 10 interface. It serves as the Internet router via Ethernet 0/1.


      When PCs on this network need to know what time it is, I want them to request time from the Netvanta 1234. Do I need to confugre SNTP to keep them happy?


      If I configure SNTP on the Netvanta 3120, must I unconfigure NTP?


      January 11, 2019 - This post has been or here for five years. I am still struggling with creating a reliable time service on the local network. I recently configured a Netvanta 3140 router to sync time from time.nist.gov. The router is configured with a name server (for DNS lookup) that exists on the Internet. Apparently Internet name services now return IP V6 addresses for time.nist.gov. It appears that the 3140 cannot accept this address and use it to SYNC NTP. I had to add a manual host entry to the router that points to the V4 address.


      Still having issues getting network switches such as the Netvanta 1544F and 1534 to sync time from the 3140. AOS versions are R13.3 or later.


      It would be great if Adtran would create an article that describes how to make this work. This should be a simple task. There is probably something that I've overlooked for five years.


      Message was edited by: Bradley Rinehart January 11, 2019 - still looking for a real answer to providing a local network time service from an Adtran router.

        • Re: NTP vs SNTP, Does Anybody Really Know What Time It Is? Especially a PC

          bcrinehart - To allow AOS devices to act as a NTP or SNTP server, you will need to enable this as it is disabled by default.


          To enable an AOS device to act as an SNTP server:

          router(config)# ip sntp server


          To enable the AOS device to act as an NTP server:

          router(config)# ntp master

          Your PCs must be configured to point to the AOS device to retrieve the time from it. So, if you want to have the PCs retrieve their timing from the 1234 via SNTP, they must point to the 1234's IP address and the 1234 must have "ip sntp server" enabled. Also, the PCs must have IP connectivity to the 1234's IP address.

          You can only have either NTP or SNTP configured at one time on an AOS device. Both cannot be enabled at the same time.

          Let us know if you have any further questions.



          1 of 1 people found this helpful
          • Re: NTP vs SNTP, Does Anybody Really Know What Time It Is? Especially a PC
            bcrinehart Past_Featured_Member



            I'm not sure that you understood my last question. Let me rephrase.


            If the Netvanta 1234 is configured to use SNTP and the Netvanta 3120 is configured to use NTP, will the Netvanta 3120 honor time update requests from the 1234?

            • Re: NTP vs SNTP, Does Anybody Really Know What Time It Is? Especially a PC
              bcrinehart Past_Featured_Member

              I recently configured NTP and SNTP on Adtran switches and routers at two different sites and here is what I've learned.

              At site "G", there is a Netvanta 1335, Netvanta 1544F and several Netvanta 1534's. The Netvanta 1335 is configured to sync it's clock with time.nist.gov using NTP. When I do a show clock details, it reports that it is synced.


              I attempted to sync the Netvanta 1544F (sntp) from the Netvanta 1335 (ntp) but the Netvanta 1544F would not sync with the NTP server on the Netvanta 1335. It appears to sync with time.nist.gov. The time display changed to the correct time but it did not display "synced" behind the displayed time.


              The Netvanta 1534's appear to sync with the Netvanta 1544F using SNTP.


              At site "H", there is a Netvanta 3120 and Netvanta 1234. The Netvanta 3120 will sync with time.nist.gov using NTP. The Netvanta will not sync with the Netvanta 1544F. I had to set up each of these two switches to get time from time.nist.gov.


              It would be great if the "border routers" could sync time using NTP with the outside world and then all other network devices could sync time from the border routers using SNTP. Maybe Adtran address this in a future release.

              • Re: NTP vs SNTP, Does Anybody Really Know What Time It Is? Especially a PC
                bcrinehart Past_Featured_Member

                New information - January 2019

                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


                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.


                host "time.nist.gov"