After reading the manual, I still could not understand what the 2nd Ethernet port (loop) is for and how it works. This is a pass-through port. I connected Metronome DSS streamer to it, so that it would be convenient to compare it with Bartok’s network board.
Are there any benefits from such a connection? Share your thoughts on this.
The dCS manual says: The Network Loop connection on a second RJ45 socket is intended for future expansion and its use is at this time unsupported.
So I second your question.
I’m curious how it is implemented, as well. Are they using a switch chip? In that case, you’d think it would also support Gigabit and not just 100mbit. Or is the network board using the Linux bridge kernel module to join two separate interfaces? Or is it not active at all right now? (I’ve never tried connecting anything to it on mine, since I have have a full switch in the same rack anyway and don’t need to do pass-through.)
Wouldn’t that work as any other loop such as think of a situation wherein there is another device (Device B) sitting close to your Bartok needing Ethernet connection, you should be able to connect loop out from Bartok to Ethernet in of Device B; you will not have to run another Ethernet cable from Ethernet switch to device B.
I believe it’s a feature of the Atheros (now Qualcomm) Integrated Ethernet Transceiver chip that’s on the Stream800 board within the Bartok.
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The question is, how much will it add noise to Bartok? And how dCS intended to use it in the future.
It seemed to me that the sound with ethernet cable directly from the router sounds a little more transparent than through this connector.
Using this Loop yesterday I listened Metronome DSS connected via AES to Bartok.
This is very convenient. Alternatively, you can connect, for example, Nucleus with Roon or another streamer to this Loop port.
Contrary to what some audiophiles imagine, “noise” on Ethernet ports/cables doesn’t operate in the same fashion as analog ports/cables or digital ports/cables, like S/PDIF, or even USB!
Ethernet ports are by design balanced and transformer coupled, so in addition to providing galvanic isolation from any upstream equipment (including an Ethernet Switch), there’s also a very high degree of transient and common-mode noise immunity.
The bottom line is that Ethernet ports/cables should be the last thing to worry about if one is concerned about noise getting into their system. IMHO, a good Power cable makes a bigger sonic difference.
Can’t speculate as to what that additional Ethernet port holds for the future. However, considering it has a different MAC address altogether from the main Ethernet port, coupled with the Cortex A8 onboard, at least on a hardware level some interesting capabilities should be possible (when coupled with the right firmware update of course). 
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I would not like to go into the topic of the influence of Ethernet cables on sound. This is an intimate topic 
But recently I connected D-Link switch between the router and Bartok and the sound became worse. I returned the direct connection back.
There is a possibility that when 2nd port is active , the Bartok will generate interference itself, i.e. do additional work using the internal processor. Perhaps this was the reason …
In general, I’m just shared my observations, and I am just as interested what plans DCS has for this port in the future.
Let’s just say the mind is a powerful thing and leave it at that 
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The main Ethernet port appears to have a TI vendor OUI. So I assume it’s the non-integrated Ethernet port on the Stream800, and instead is using the external RGMII Ethernet connection. The Ethernet PHY on the Stream800 is presumably the 10/100 port on the Bartok. This suggests they are using the Linux kernel bridge module to link the two ports together. This means forwarding between the two ports will use a small amount of CPU on the network board.
If I’m not mistaken, there’re two Atheros Ethernet transceivers; a 10/100/1000 capable AR8035 for the main Ethernet port, and a 10/100 only AR8030 for the Loop port; both RGMII/RMII’ed into the TI Sitara on the Stream board. Independent, but bridged in software. 
You clearly have a far better understanding of this issue that I. Are you saying that both of these ports are active, one Gb and the other 10/100. Can one use the loop port for, say, a Roon Nucleus and the other for network connection?
Short answer is Yes.
Plus using the port wouldn’t cause any detrimental effect on sound quality either. Contrary to some suggestion in this thread, there’s no added CPU processing involved that could have any impact on sound quality because the bridge code is built into the Linux kernel running on the networking board; Instantiating bridged ports just allows packets to flow between them (even a $50 Raspberry Pi can handle bridging ports without taking any hit to the CPU 
).
There a couple of caveats though IMHO;
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If you Power Off your Bartok, then connectivity to the rest of your network is lost. So, if you intend to use the Roon Nucleus for other end-points with the Bartok off, it won’t work. Sleep mode is fine though.
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I don’t expect you’ll get any benefit at all from using that port. All it’ll do is save you one port on your main Ethernet switch, while adding restrictions on how you use your Roon Nucleus.
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dCS clearly marks the Loop port as “intended to be used… to other dCS units.”; how things work could change in future firmware upgrades that might impact your use of that port for a Roon Nucleus.
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This is my question on the loop port to the community and replies. Hope it is useful.
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I would add to your list that if your Nucleus hold an internal music storage device that you often update with new local music, having it on a 100mbps connection will severely limit your transfer speed.
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i plugged Upnp server to the loop port. It works. But if file is uploaded to Upnp server, the upload is not stable and very slow
Hi,
May I please take this opportunity to bring your attention to the fact that in the current dCS firmware the network “Loop” port is unsupported and its functionality has not been defined by us so you should not be using it to plug in network servers etc. as the way that port functions may be changed by future firmware releases if we do decide to implement specific functionality on that port.
As such, the use of that port for end user purposes is strongly discouraged.
BR
Phil
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Sounds like there’s something on the way 
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Hi Omni,
In the manuals for the Bartok (and the Rossini) we simply state that “The NETWORK LOOP connection is not supported” so we could, for example, turn off that port in a future firmware update as we don’t use it for anything ourselves and we don’t support using it for anything - such as hanging a UPnP server off it.
Hi All,
The information in this thread has been raised as being confusing and open to interpretation so I’d just like to take the opportunity to clarify that the functionality for the “Loop” port on the rear of the Bartok and Rossini is not defined and as such we may decide to use / repurpose / disable that port in the future.
It should not be used to connect NASs, audio servers, Roon Cores or other devices to your network.
BR
Phil
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