Older Zigbee Routers going offline

Backgound: We have Zigbee deployments that range in age from 10 years old to brand new, so we have Digi modules of various vintages. They all run Zigbee, with a coordinator and 50-300 modules programmed as routers, no end devices as power consumption is not important. We use Realport to move data back and forth to our data center.

The newer Zigbees that have firmwares in the “4060/4061” range do not seem to suffer.

However, older Zigbees Pros (of various model codes) with 23A7 firmware seem to exhibit the following failure frustratingly often.

As long as the coordinator is present, they will hold a connection for literally years. However, if the coordinator is removed or powered off for any significant length of time (a day or two), then when the coordinator returns, some nodes will not rejoin the network unless power cycled. (or software reset with the FR command but this is not feasible when the module is “lost”)

Question, is this a known failure mode?

And bigger question, for our nodes that are in a faraway city in an inaccessible location, is there a way to get these modules to reconnect? Are they stuck on the wrong channel and no longer looking for a network? Waiting for a magic network signal that will cause them to come alive again?

Especially because of COVID restrictions, we have quite a few nodes that are out there that are offline and not physically serviceable.

Any help or similar experience appreciated.

Set the NW on them and that should take care of it. Note that this is not a bug but expected behavior as the Coordinator is not expected to be powered off.

Thank you for your assistance!

Sorry I should have said this in my question, but I have NW set to 0x20.

Most of the time the routers will reconnect, and I have even changed coordinators after Connectport failures and the network will reform.

Just a few stubborn ones don’t, but the number is growing “out there”.

I have recreated the problem at my house, and that’s how I learned that I can locally send an FR command to the lost router it will reconnect. Otherwise it just sits on 0xFFFE.

I’m putting timeouts and the FR in future revisions of code, but that doesn’t help the ones that are out there. :frowning:

I would suggest if you can reproduce the issue, is to submit a case to Digi support with all of the steps needed to reproduce the issue with. This way, it can be addressed.