Hi everyone, I could not find this topic in the forums, so I was wondering if someone could help me with this.
I have the Roon Server on an iMac and I do not use ARC in any other way but to load the ARC with some downloaded tracks and use it in Offline mode when travelling.
I still have the port at a certain numerical value (see below - port redacted), but my question is, should I put this at zero or any other value so that the port is made unusable for the purposes of using ARC?
Thanks all!
The redacted port that you are using canāt work because according to the message it is used by something else. It may not matter if you are not trying to use ARC in online mode, but be aware that there seems to be something else on your network that has a port open.
You can set it to 0 in the Roon ARC settings if you donāt want to use ARC online at all, but the exact same thing is accomplished by not creating a port forwarding rule for ARC on your router (or by not using UPnP on the router) in the first place
Hi Suedkiz, many thanks for your reply - much appreciated.
Does not sound good something else is using the port! Will have to check. In the meantime I have set the port for ARC at zero.
Many thanks again!
Itās possible that someone Roon just got confused with this message, but probably worth checking what is going on
Any application you run that uses ip can choose to use port 55000. It is not, according to any standards, a reserved port - which is why Roon choose it for a default port and also why Roon allow you to change it.
Something other than Roon using Port 55000 is not a problem per se. It just means that you have to use a different port number - somewhere between 1024 and 65535 (1-1023 are reserved ports) - that is not already in use.
While this is true, of course, I took @Henkemannenās desire to disable ARC entirely as an indication that they donāt want any open ports at all, and if this is the case they might want to investigate what it is that has an open one.
From my limited understanding of how it works and trying to understand your use case.
1. Set a port or leave default. This will turn ARC āonā. You need it on to use it locally for your downloaded music.
2. On your router make sure UPnP is off. This prevents Roon from auto configuring your router.
3. Make sure you have no port forwarding rules related to that port on your router.
4. Make sure you have no āallowā rules on your router for that port.
5. Your Roon ARC settings screen should look something like this:
And, when you login to ARC, it should say something about only working locally. If your super paranoid you can run an internet scan on your public / WAN IP and make sure it doesnāt respond.
After further testing consider the above rubbish. Do this:
ARC works on the local LAN without any open ports on the router, but does it get turned OFF entirely when entering 0 as the port number? I never tried this
ARC works with TCP. It still needs a port open. What port is it using if you set ARC to 0?
I donāt know, it might actually use 0 and then it would stop working, or it might ignore it and use whatever other port for the internal connection as all ports are typically open internally on a LAN. I had clarified my previous comment while you were writing your reply 
Just testedā¦ Its working with setting port 0 although Iām not troubleshooting further to identify what port its using. Iāll edit my post above as setting 0 should be the right answer now that I actually tested it. I should have done that before answering. Thanks for challenging me. One day Iāll do a packet capture and look at the port its using locally.
Not to derail but this is not the right way to think about about ports. A service or server listens for incoming connections. The network stack knows to feed data off the network to the application (its not feed, the app has to retrieve it but Iām simplifying my response here) based upon the port. Yes, there are āknownā ports for various services and there is a international organization which has assigned different services different ports but thats not enforced anywhere. You can run any service on any port. Additionally, you can run no services meaning your machine wonāt be listening for anything and network packets arriving at the machine will simply be dropped.
Like yourself, it appears, I have never tried local network ARC operation with the port set to 0.
As a consequence, reading the OPās requirement to use ARC locally for downloading files, but to fix the āport already in useā issue, I provided the solution that I knew would allow local access (and external access, with the addition of uPnP or an explicit port forwarding rule, if they wished).
I have subsequently performed an experiment, and local network ARC connectivity does appear to work with the port set to 0 - so either solution would achieve the OPās goals.
I was trying to keep it short fĆ¼r the purposes of this thread I meant simply that in a normal home LAN there is usually nothing that is blocking an open port if a server somewhere has an open one (in the way a router does block them on the internet interface). So the ARC app and Roon Server are free to use whatever ports they want to on the internal LAN, as Roon explicitly does not support VLANs, managed switches, or other LAN configurations that might get in the way.
Thanks all for your replies and taking your time testing!! Very much appreciated. I have now set the port to 0 (which is working nicely.)
Thanks again.
Henkemannen
