For now I think we indeed can conclude that all DNS-resolving is done using IPv4 
@PA0MMV As most sensors use our āoriginalā firmware there will be only very few sensors using IPv6. Our firmware doesnāt support IPv6.
@Phaze-III
I take part in a bĆØta test groep of my provider that tests firmware for the Sagemcom cable modem/router. So I frequently get firmware updates. During the update internet acces is interupted for a short time. Last time the sensor did not sponteanously recover. I could still Connect to its internal web interface but it could no longer Connect to the community servers. Presumably when the cable modem came back on line IPv4 was up before IPv6 which caused a permanent failure to connect to the (IPv6) servers. Rebooting the sensor solved the problem.
@PA0MMV
My cable modem/router also gets the occasional āupdateā from Ziggo (mostly resets) and usually my sensors can gracefully reconnect after the interruption. I understand that in your case it normally also goes well except for this one time.
Did you by any chance get a new IPv6-prefix (and/or external IPv4) address after that last update?
@Phaze-III
Do you also have the IPv6 version installed?
Actually this is the first modem update since I installed the IPv6 version so I can not tell what is ānormalā. I wil take a Good look at what happens with the next update.
And yes, this time I got a new IPv6 prefix. That happens occasionslly, most of the times of stays the same. IPv4 did not change.
I also run the IPv6 version (of course 
) I think what happened in your case is that during and after the router-update the sensor still had an IPv6 address within the old prefix active and didnāt pickup the new prefix or something like that.
@Phaze-III
Sounds plausible.
Does the sensor listen for router advertisements periodicly or only at startup?
Iām wondering the same. Based on your report it could be the latter but it might as well be that the āoldā prefix wasnāt expired yet (i.e. the modem didnāt withdraw the prefix before updating). As mentioned earlier this (i.e. how the used framework/library handles the various IPv6 autoconfiguration setups) is something that needs further investigation.
@Phaze-III
I seriously doubt this is a router issue. I have had native IPv6 from this provider since 2016 and over the years had several IPv6 capable devices connected 24/7. I have never seen this behaviour before when the prefix changed. At the moment the only other device connected 24/7 is a Ripe Atlas probe. It picked up the new prefix without problems.
I didnāt mean to blame the router Even if the router would do a āprefix deprecationā before shutting down and if the sensor would process the relevant RAās it still could take a few hours to āforgetā the old prefix.
And please keep in mind that the RIPE Atlas probe uses a well tested and capable OS and network stack. The sensor firmware, or better the Arduino framework and especially the IPV6 network stack isnāt that well tested and very lightweight (it runs on a simple controller with limited capabilities and resources). So I donāt expect that it will do the right thing in every possible situation (and with IPv6 the possibilities are almost without limit 
Thereās a nice discussion about exactly this situation on Reddit - Dive into anything
On a related note, do you use DHCPv6 or SLAAC on your router?
DHCP6 is not enabled on my router. SLAAC is.
According to the grape vine I Will recieve a router update Wednesday night. I will Watch it closely.
@Phaze-III
The announced router update was received and processed betweem 04:38 and 04:44 this morning. The IPv6 prefix was not changed. The sensor recovered but changed the connection from the WiFi access point nearest to it ( 3 meters) to the WiFi of the modem itself (15 meters). This is a quirck in the providerās smart WiFi system that I already observed and reported to the provider some month ago.
After restarting the sensor it went ito AP mode. And after 10 minutes it reconnected to the nearest WiFi access point.
That is what I have to report for now.
@Phaze-III
Tonight there Will be another modem/router firmware update. Stay tunedā¦
@Phaze-III
Router update received 7 Aug 04:59.
IPv6 prefix not changed and sensor remained on-line. Nothing else to report.
@PA0MMV
Thanks for the updates. I see similar results when my modem is remotely restarted by the provider (Ziggo) or when I do either a soft reset (via the WebUI) or a hard-reset (power-down/power up). The sensor loses the connection but will just reconnect after the wifi is available again.
You also wrote earlier:
Does this happen always when restarting the sensor?
@Phaze-III
Yes, going into AP mode first after a restart happens every time with this version. During the last week I had to take down the sensor several times because the place where it hangs needed a painting job. I took the opportunity to watch it carefully at every restart and every time it went into AP mode first.
@Phaze-III
I received an email from my provider that my modem/router will be rebooted in the next hours. The IPv6 prefix may or may not change. At the moment I am on a camping in Bad Bentheim Germany and the Wifi is IPv4 only. So it will have to wait until Monday until I can report on the effects.