5 ms·

After the Telstra NTS issue and preparing for the upcoming summer storms and power outages, I set up a chrony mesh on three devices, each with a different upstr

After the Telstra NTS issue and preparing for the upcoming summer storms and power outages, I set up a chrony mesh on three devices, each with a different upstream stratum 1 NTS. I seriously considered a GPS reference too, but I live on the bottom floor of apartment blocks so reception is probably quite poor. After blocking the firewall ports, the mesh stays linked and drift is well within sensible boundaries for the typical length of internet and power outages of a few hours. Although, a man with a watch knows the time but man with two watches cannot be certain.

Palomides 9d ago
I have a GPS based PTP server, the antenna is indoors 15 feet away from a south facing window, it locks on pretty well (though this will probably depend on the surrounding buildings)
- geerlingguy 9d ago
  It's surprising how often I can get an okay-ish GPS signal indoors... it seems to have a lot more to do with building materials than anything else. Multipath reflections means the location (and thus timing accuracy) wanders a lot, but it's still great down to microseconds if you can get 5+ satellites in view.
anitil 9d ago
This sounds pretty interesting - what are you working on where it's necessary to maintain this level of time precision? I've worked on positioning systems where it's obviously important, but it never mattered much at home
- itchingsphynx 9d ago
  Nothing special - just a homelab. It's not so much the precision that matters at home as for planning when the home becomes an island, in 'orphan mode' as chrony calls it [1], without a time reference at all. Time really is a 'sovereign function' per Telstra's report [2], especially if you have internal HTTPS, etc. Last summer an 8+ hour mains power outage drained my home CWWK OPNsense router's UPS then internal battery (it must have been losing voltage). When mains power came up the router was unable to connect to the ISP because the internal time was completely wrong and I had to manually set it via console. However, the internal batteries and clocks on other home network infrastructure (HP NAS and Lenovo Tiny) were fine. The chrony.conf orphan mode: server 192.168.1.1 server 192.168.1.2 local stratum X orphan (higher X determines who is master in orphan mode, usually minimum 10) Annoyingly, the OPNsense chronyd plug-in does not (yet) implement the "local orphan" mode [3], so I have not yet confirmed that it does accept the non-reference master orphan time to bootstrap itself... should test before the summer storms start again. 1. <https://chrony-project.org/doc/latest/chrony.conf.html https://chrony-project.org/doc/latest/chrony.conf.html> 2. <https://www.telstra.com.au/exchange/what-we-ve-learned-from-the-external-investigation-of-our-july-o https://www.telstra.com.au/exchange/what-we-ve-learned-from-...> 3. <https://github.com/opnsense/plugins/issues/5115 https://github.com/opnsense/plugins/issues/5115>
  - anitil 7d ago
    Ah I see in my head I expect blackouts to be a few minutes, so I hadn't thought what would happen after several hours. When I was in the embedded world I used to explain that https implies a whole lot of infrastructure that isn't obvious at first for this reason (and also that cert rotation implies the ability to update the firmware or some filesystem which isn't always the case).
- ErroneousBosh 9d ago
  If we're going to be stupid with it, I should write up an article on my ultra-precise 16MHz Arduino that runs at cock on 16000000Hz. The crystal is replaced by a GPS-disciplined VCO. Why? Well, I wasn't doing anything else much fun...

Palomides 9d ago

I have a GPS based PTP server, the antenna is indoors 15 feet away from a south facing window, it locks on pretty well (though this will probably depend on the surrounding buildings)

geerlingguy 9d ago
It's surprising how often I can get an okay-ish GPS signal indoors... it seems to have a lot more to do with building materials than anything else. Multipath reflections means the location (and thus timing accuracy) wanders a lot, but it's still great down to microseconds if you can get 5+ satellites in view.

anitil 9d ago

This sounds pretty interesting - what are you working on where it's necessary to maintain this level of time precision? I've worked on positioning systems where it's obviously important, but it never mattered much at home

itchingsphynx 9d ago
Nothing special - just a homelab. It's not so much the precision that matters at home as for planning when the home becomes an island, in 'orphan mode' as chrony calls it [1], without a time reference at all. Time really is a 'sovereign function' per Telstra's report [2], especially if you have internal HTTPS, etc. Last summer an 8+ hour mains power outage drained my home CWWK OPNsense router's UPS then internal battery (it must have been losing voltage). When mains power came up the router was unable to connect to the ISP because the internal time was completely wrong and I had to manually set it via console. However, the internal batteries and clocks on other home network infrastructure (HP NAS and Lenovo Tiny) were fine. The chrony.conf orphan mode: server 192.168.1.1 server 192.168.1.2 local stratum X orphan (higher X determines who is master in orphan mode, usually minimum 10) Annoyingly, the OPNsense chronyd plug-in does not (yet) implement the "local orphan" mode [3], so I have not yet confirmed that it does accept the non-reference master orphan time to bootstrap itself... should test before the summer storms start again. 1. <https://chrony-project.org/doc/latest/chrony.conf.html https://chrony-project.org/doc/latest/chrony.conf.html> 2. <https://www.telstra.com.au/exchange/what-we-ve-learned-from-the-external-investigation-of-our-july-o https://www.telstra.com.au/exchange/what-we-ve-learned-from-...> 3. <https://github.com/opnsense/plugins/issues/5115 https://github.com/opnsense/plugins/issues/5115>
- anitil 7d ago
  Ah I see in my head I expect blackouts to be a few minutes, so I hadn't thought what would happen after several hours. When I was in the embedded world I used to explain that https implies a whole lot of infrastructure that isn't obvious at first for this reason (and also that cert rotation implies the ability to update the firmware or some filesystem which isn't always the case).
ErroneousBosh 9d ago
If we're going to be stupid with it, I should write up an article on my ultra-precise 16MHz Arduino that runs at cock on 16000000Hz. The crystal is replaced by a GPS-disciplined VCO. Why? Well, I wasn't doing anything else much fun...