Backbone network needed?

[bkoblenz]

I am pretty new to this stuff so maybe I just don't understand.

I am crafting my own "hub" for matter devices and there are two things that confuse me:

1. I am not sure why the INFRA_IF_NAME needs to be specified. In particular, if all control is managed locally to the device running the OTBR then why is a "backbone?" network required? In particular, when that backbone network was unavailable, none of my matter devices were discovered? Is that expected behavior?

2. For my device, the actual backbone network is not really known at OTBR build time. It might be wlan0, it might be eth0 and there are actually a couple of other interface names it might be. So I would really like a way to dynamically specify the backbone network. It seems that /etc/default/otbr-agent contains the reference to the backbone network interface name (not sure if there are other places). Might it be sufficient to modify that configuration file dynamically and restart the otbr-agent to get the dynamic backbone I am looking for?

[superwhd]

1. I am not sure why the INFRA_IF_NAME needs to be specified. In particular, if all control is managed locally to the device running the OTBR then why is a "backbone?" network required? In particular, when that backbone network was unavailable, none of my matter devices were discovered? Is that expected behavior?

A Matter hub discovers services via mDNS on the infra network of your Thread Border Router. If your infra link is down, your Thread Border Router's mDNS provider may not properly advertise the services for your matter devices. Therefore the hub may not be able to discover the services.

2. For my device, the actual backbone network is not really known at OTBR build time. It might be wlan0, it might be eth0 and there are actually a couple of other interface names it might be. So I would really like a way to dynamically specify the backbone network. It seems that /etc/default/otbr-agent contains the reference to the backbone network interface name (not sure if there are other places). Might it be sufficient to modify that configuration file dynamically and restart the otbr-agent to get the dynamic backbone I am looking for?

You can specify the backbone network interface name for otbr-agent by command line argument -B. So your idea of changing the configuration and restarting otbr-agent should work.

Alternatively, there's an InfraLinkSelector module which allows you to pass in multiple -B arguments and it will select one of the backbone interfaces to use, according to the interfaces' status. You can also implement your custom selector logic at otbrVendorInfraLinkSelect if you enable OTBR_ENABLE_VENDOR_INFRA_LINK_SELECT.