Join an existing mesh Network with a mesh provisioner (nrf mesh sdk)

[neicureuil]

Hi,

Is it possible to join an existing mesh network with a provisioner made on Nrf52840 (s140)  ?

I have used the provisioner example to make a provisioner which actually create a new mesh network. But after an "erase all" of the board, the provisioning data are lost and the board can't reconnect to the network because information are lost during the erase (logic).

Is there a way to extract the provisioning data and mesh network data from the board to use them later on an other board ?

My goal is to create a mesh network with a device, then store in a file all the information related to this network to be able later with another board to join this network and add new devices.

I have setup a serial connection to send data through the usb port to my computer so I could retrieve and return the data by this method.

I know that this is possible in the mobile application with the "export network" and "import network" functions but I can't reproduce the functionality with the mesh SDK.

Is this possible? If yes how?
Regards

Used sdk :

- nRF5_SDK_16.0.0_98a08e2

- nrf5_SDK_for_Mesh_v4.2.0_src

Board used :

- nrf52840 evaluation board

- nrf52832 evaluation board

[Hung Bui]

Hi Neicureuil, 

I would suggest to have a look at this similar case here: https://devzone.nordicsemi.com/f/nordic-q-a/77056/i-want-to-recover-control-provisoned-device-when-i-reopen-the-pyaci-script-and-reset-the-52840-dk

Note that what you are trying to do is not something we have tested and also not defined in the spec on how it should work neither (multiple provisioners sync up).
So this would require you to study the code thoroughly to implement what you want to do and should be able to debug it. We will try to help you along the way but we are having limited resource at this moment due to Summer holiday in Norway. 

Regarding your question, as I mentioned earlier, you won't be able to talk to the configuration server from your client without the dev key. It's like the application key specifically for the configuration server on the node. 
Without the dev key (s) you won't be able to configure the node (s). 

 The time it take of 5 minutes to be able to talk to the network is a bit strange. I would need to talk to the team on why it take this much of time. 

[neicureuil]

Hi,

Thanks for your answer, the export and import of the device dev key works ! The config model now works fine. Thanks.

Is there any way to change the devkey generation for the nodes (my nodes use the "light_switch_client" example from the mesh sdk), (I have do it for my provisioner but I don't find where its done for the node) ?

Will it be possible to be kept informed about the 5 minute delay ?

Regards.

[Hung Bui]

Hi Neicureuil, 

As far as I know the device key is generated in prov_utils_derive_keys() in prov_utils.c if you are using the provisioner or the serial example. If you use the phone you would need to look into the app code. 

But note that, there is a rule about how the device key should be produced in the Bluetooth Mesh spec. Changing that risk the chance that your device won't be able to qualify and it would increase  security vulnerability. 

[neicureuil]

Hi,

Thanks for the answer, temporally I have override the devkey generation function by a custom one based on the device mac address and uuid, so I can recreate it in the mesh network reload process.

Otherwise, can the provisioner update the devkey of the node after the provisioning process or once the key is set, it cannot be changed ?

My issue of the IV index delay can it come from my mesh sdk version (4.2.0) ?

Regards.

[Hung Bui]

Hi Neicureuil, 

I don't think it's possible to change the devkey. You would need to reprovision the node to get a new devkey. 
I'm still waiting for the mesh team about the question about the 5 minutes delay for IV index update.