RAAT and Routing

I’m using Ubuntu 18.04 with the MSB Renderer, and my question pertains to the Ubuntu bridge and RAAT (and perhaps lower level protocols). Would you please address the following question to your Linux experts?

My Ubuntu server (with Roon Core) has a dual Ethernet card, both connections slaved to a bridge in Ubuntu, with one slaved connection to the LAN and the other to the renderer. In theory this configuration provides a direct Ethernet connection between Core and renderer, the sonic benefits of which are well documented on computeraudiophile.com. I created the bridge with nm-connection-editor in Ubuntu, taking the defaults.

Question: Will RAAT in fact route directly from Core to renderer over the slaved connection? I’ve asked this three times on Ask Ubuntu with no responses, and I’ve now posed the question here for the third time. I suspect few can answer this with certainty. Linux documentation states bridges function at Layer 2, and therefore I believe should take the shortest path to target IP, but I’m not certain.

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If everything is on the same subnet, I think there is a possibility to make it work if you manage to configure the bridge to pass all multicast packets, which may require some non-default parameters. Google searches reveal people tend to have problems with the default behavior of multicast snooping. If you need RAAT to “route”, then it certainly won’t work.

Since you already have the hardware and have already setup the bridge, is it working or not?

Depends on what you mean by “working.” Yes, the packets make it to the renderer through the bridge, but the question is the exact path they take. Do they go out and back in again? The “Layer 2” aspect would suggest they do not go out to a higher layer first, but I need someone knowledgeable about how bridges function to confirm. I need definitive input from someone with the knowledge.

I believe you’re indeed taking the shortest path.

As for “working”, it means you can see your network endpoint in Roon, can control it and hear music from your setup without any abnormal audio dropout or distortion at the highest possible sample rate that your endpoint / DAC supports.

Yes. In fact, the transitions between files of even different rates are super fast, but then I might attribute that to the superb engineering of the MSB Select II DAC, as the transitions with the same server were not so fast with the dCS Vivaldi DAC and Network Bridge endpoint.

Peter, thank you for being kind enough to respond. Do you program networked music players?

My team and I make firmware for Lumin Roon Ready network music players.

The only other thing I have to add is that in taking the defaults for the bridge, in which the IP4 Tab in nm-connection-editor indicated DHCP, the slaved connection to the network ends up with a static IP (though none was specified), and the slaved connection to the renderer is dynamic. I found this interesting.

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