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

[Anonymous]

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.

[Anonymous]

- 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.

Thanks,

Noor

[Anonymous]

I understand the need to configure. I believe that NIST does both. I can determine that and configure accordingly.

However, what I need to know is if PCs prefer NTP or SNTP or don't they care?

On a Windows 7 machine, I went into the clock, selected the Internet time tab and pointed it at the 3120's VLAN interface address. I told ot to sync now but it would not sync. I also pointed it to nist.time.gov and it would not sync. I pointed it at time.microsoft.com and it synced (of course). NIST documentation says that PCs should accept NTP but that did not seem to work.

Do you or anyone reading this have any experience getting a PC to sync time from NTP on a Netvanta VLAN interface?

[Anonymous]

- From what I've seen online, it appears that Windows PCs use NTP as you mentioned. You may be able to get more information by enabling the NTP debug on the AOS device. This can be done with the command "debug ntp".

Let us know if you have any further questions.

Thanks,

Noor

[Anonymous]

I did more research via the Adtran manuals and also did some testing via routers and switches. The 3120 supports NTP and SNTP. However, it appears that the Netvanta 1234 only supports SNTP. I can't locate any NTP configuration commands on the 1234.

So, maybe I'm wrong about PCs looking for SNTP.

Also, you can't enable both NTP and SNTP on the 3120 at the same time. A decision has to be made. Any input on which protocol it should be?

[Anonymous]

You are correct in that NTP is not supported on the 123x switches. Unfortunately, we are unable to answer questions regarding your PC settings. However, you should be able to check with your OS vendor support to confirm the behavior of your PCs.

The protocol you end up choosing is to your preference. Generally, NTP provides the advantage of being more accurate. However, the protocol you choose depends on the needs of your networking equipment that will be pulling time from the server.

Thanks,

Noor

[Anonymous]

If SNTP is configured on the Netvanta 1234, can it receive time updates from a Netvanta 3120 that is configured to use NTP? 

[Anonymous]

@bcrinehart - No, the 1234 would not be able to receive time using NTP from the NetVanta 3120.

Thanks,

Noor

[Anonymous]

Noor,

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?

[Anonymous]

@bcrinehart - Sorry for the confusion. No, the 1234 will not be able to get time updates from the 3120 if the 3120 is configured to use NTP. Since NTP and SNTP cannot be used at the same time on an AOS device, its not possible to have the 1234 (which only supports SNTP) and your PCs (which may support only NTP) to get their time updates from the 3120. The only way this scenario could work is if the PCs support SNTP. Then the 3120 could be configured for SNTP and that would allow the 1234 and the PCs to get their timing updates from it.

Thanks,

Noor

[Anonymous]

When configuring DHCP pools, the only option for a time server is NTP. Does this indicate that devices such as PCs that get addresses via DHCP typically support NTP and not SNTP?

[Anonymous]

@bcrinehart - For an IPv4 DHCP pool in AOS, the 'ntp-server' command or field corresponds to either an NTP or SNTP server. The option field in the IPv4 DHCP packet is the same. It is up to the client and/or SNTP/NTP server to determine whether to use the NTP or SNTP protocol.

This behavior differs for an IPv6 DHCP pool in AOS. There are two separate commands within the DHCP pool to input either an NTP server or an SNTP server. The reasoning for this is that IPv6 supports additional options for NTP servers that it does not support for SNTP servers.

Let us know if you have any further questions.

Thanks,

Noor

[Anonymous]

- I went ahead and flagged this post as “Assumed Answered.”  If any of the responses on this thread assisted you, please mark them as either Correct or Helpful answers with the applicable buttons.  This will make them visible and help other members of the community find solutions more easily.  If you still need assistance, I would be more than happy to continue working with you on this - just let me know in a reply.

Thanks,

Noor

[Anonymous]

Noor,

There are still unanswered questions regarding the relationship and compatibility between NTP and SNTP. Ideally, I would like to see a "hot to" white paper on these time protocols.

What is the relationship between SNTP and NTP. When do we use NTP vs SNTP?

Brad

[Anonymous]

Brad,

In simplest terms, the relationship between SNTP and NTP is that SNTP is a subset of NTP. There are certain requirements SNTP is not forced to meet that NTP is. The RFC will probably be the best source of information regarding SNTP and NTP. I've provided a link below:

http://tools.ietf.org/html/rfc5905

Thanks,

Noor

[Anonymous · Accepted solution]

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.

[Anonymous]

It's been almost a year since I started this thread. Just wondering if there is any effort at Adtran to add the feature to allow a router to sync time with an NTP source and then act as both an NTP and SNTP server.

At several of the sites that I manage, there is a need for time consistency. There are cameras, video recorders, servers that perform industrial data collection, electronic time clocks, card access systems, etc. All of this equipment requires a standard time source. While all can be pointed at an external time source, it makes more sense to allow one or two routers to sync with an external time source and then pass that information along to other devices inside the LAN.

[Anonymous]

Not sure where your seeing issues with this but I've got several sites setup to work this way. In IP services make sure you have it checked for SNTP time server and send unsynced if you need that. Almost all of my installs I have a 3120/3448 as the router and several switches/phones/servers getting time from the router.

[Anonymous]

-  would like the ability to use SNTP and NTP functionality on an AOS device at the same time. Currently, AOS does not support this. Either NTP or SNTP can be enabled at a given time.

Let us know if you have any questions.

Thanks,

Noor

[Anonymous]

- At this time, there are no plans to add such a feature to AOS. I would suggest contacting your Adtran Sales representative and letting them know about your need for this feature.

Let us know if you have any questions.

Thanks,

Noor