NTP only uses port 123

The simple answer for NTP servers is anything because accuracy is going to be within 1s regardless of what you use (and there are all sorts of debate about accuracy of servers and latency). Obiously lots of devices such as CCTV will have a default such as pool.ntp.org or time.windows.com in them already, or you could use nz.pool.ntp.org if you want NZ based servers.

Interval is something you need decide on yourself.

I usually use: nz.pool.ntp.org 

Two options:

https://ntp.net.nz/

https://www.cloudflare.com/time/

4x NZ NTP Servers - https://www.pool.ntp.org/zone/nz

I don't let my cameras out to the Internet so they can't contact any of the Internet based NTP servers.

Rather than create a specific firewall policy allowing NTP, I have just pointed the cameras at my firewall which is also an NTP source (It is connecting to nz.pool.ntp.org)

i use nz ntp pool on router, and then distribute ntp over dhcp (option 42)

that keeps the network almost perfectly inline and cuts any jitter to it.

for cameras etc that need it, their packets only travel as far as the router.

at some stage i intend to fire up a gps ntp server and add it to my local pool.

hio77:

 

i use nz ntp pool on router, and then distribute ntp over dhcp (option 42)

 

 

 

that keeps the network almost perfectly inline and cuts any jitter to it.

 

for cameras etc that need it, their packets only travel as far as the router.

 

 

 

at some stage i intend to fire up a gps ntp server and add it to my local pool.

 

I just want you to know that I've now started investigating cheap GPS Modules that I could attach to my RPi to add GPS NTP to my network...

toejam316:

 

I just want you to know that I've now started investigating cheap GPS Modules that I could attach to my RPi to add GPS NTP to my network...

 

Your welcome

If accurate time is significant for you, I recommend that you use the same provider (but with different servers) to get your time from. This will ensure that they all handle the leap seconds in the same manner as there is no standard on how this should be implemented.

If you can handle being out by a second, then ignore this post.

fyi, the next Leap second appears likely to be on the 30th of June this year but still to be confirmed.

toejam316:

 

I just want you to know that I've now started investigating cheap GPS Modules that I could attach to my RPi to add GPS NTP to my network...

 

Just be aware that GPS Time is not the same as UTC.

GPS Time is an engineering concept, UTC is an astronomical concept.
GPS Time does not have Leap Seconds, UTC does have Leap Seconds, hence GPS and UTC are currently different by exactly 19 seconds. The next Leap Second is currently scheduled for insertion between 23:59:59 and 00:00:00 UTC (i.e. there will be a 23:59:60 second) on 30 June 2020

You can buy GPS-linked NTP source 'clocks' that know about this, but they tend to be not too cheap - a top-end device like the Meinberg IMS-Lantime-M1000 cost several thousand dollars the last time I was involved in buying one 😮.
I'm not sure how the home-built / amateur market handles this, I would be interested to know.

BTW, if you use a GPS NTP server, you should be able to get your device time synchronised to with in a few tens of milliseconds, the NTP protocol is that good!
😀

PolicyGuy:

 

Just be aware that GPS Time is not the same as UTC.

 

GPS Time is an engineering concept, UTC is an astronomical concept.
GPS Time does not have Leap Seconds, UTC does have Leap Seconds, hence GPS and UTC are currently different by exactly 19 seconds. The next Leap Second is currently scheduled for insertion between 23:59:59 and 00:00:00 UTC (i.e. there will be a 23:59:60 second) on 30 June 2020

 

You can buy GPS-linked NTP source 'clocks' that know about this, but they tend to be not too cheap - a top-end device like the Meinberg IMS-Lantime-M1000 cost several thousand dollars the last time I was involved in buying one 😮.
I'm not sure how the home-built / amateur market handles this, I would be interested to know.

 

 

 

BTW, if you use a GPS NTP server, you should be able to get your device time synchronised to with in a few tens of milliseconds, the NTP protocol is that good!
😀

 

Both Chrony and ntpd know about this, as long as you update the package containing the timezone data at least every six months.

-e- The six months is because leap seconds are only announced about six months in advance.

toejam316:

 

I just want you to know that I've now started investigating cheap GPS Modules that I could attach to my RPi to add GPS NTP to my network...

 

Make sure you get one with a PPS output (pulse per second), otherwise you're better off using an internet NTP server.