ARC issues on Asus RT-AX88U

Roon NUC

Network setup:

Fritzbox as a source modem with port fwd setup for Ch 55000

Asus RT-AX88U as Router running a mesh network in a large house,

settings in WAN tab of the UI, with simple port FWD rules.

Connected Audio Devices

Roonready NAIM Uniti Atom

Number of Tracks in Library

66,000 Tracks in library mostly FLAC

Description of Issue

Hi All, Ive been trying to connect to allow ARC to pass through my ASUS RT-AX88U but having no luck whatsoever.

Error below:
getting the below error:

“connectivity”: {“status”:“NetworkError”,“status_code”:504,“error”:“error: Error: ETIMEDOUT, response code: undefined, body: undefined connected? undefined”},
“external_ip”: {“actual_external_ip”:“”,“router_external_ip”:“”},
“status”: “status”: MultipleNatFound
“natpmp_autoconfig”: {“status”:“NotFound”},
“upnp_autoconfig”: {“server_ip”:“”,“found_upnp”:true}

the setup appears very simple, Ive opened ports for other applications but this error I don’t understand at all.

Help massively appreciated as Im sure you are very busy right now.

Thanks for reading

Hi Levi,

The error messages tells us that there is MultipleNAT in your configuration. That’s the problem ARC isn’t working. I’m not an expert on this subject but may this helps you (in the article there is a section of MultipleNat).

Hope it helps.

Kind regards,


many thanks Maarten I will review this.
thanks again.

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I think the solution might be to put the Fritzboz into Bridge mode, this is described as

" . Enable PPPoE Passthrough"

Can I check with anyone who might know if doing this would resolve the multiple NAT issue? Im keen not to change anything that Im not an expert in and could cause issues downstream?

Hi Levi,

Not an expert myself, but see screenshot below (option 2 first line). If you put the Fritzbox in Bridge mode and it’s not working, you set it back to the setting before you make the adjustment. Just make a screenshot and save it.


I would agree you have a double NAT, and your solution is correct to place the Friztboz in bridge mode , you will then need connect to your ISP with your login details via the Asus RT and then activate UPNP or add the port forward rule to the Asus RT

Many thanks for the support here, I will try this now.

Bridge mode alone was not sufficient to fix the problem, not for me. So, I attempted to explain the steps I took and settings to finally get this working, at least using the same modem as you.

None of that will help as your ISP is using CGNAT.

You need to ask them to turn off CGNAT or assign you a static public IPv4 address

Well a public IP, not necessarily static.

Thanks everyone, I will call POST Luxembourg, hoping it wont be a problem for them to share this.

Turning off CGNAT will enable a (DHCP) public IP if they can’t do that then assign a static IP

Pretty much what I said :roll_eyes:

1 Like

Hey @Levi_Boorer1,

You have my sincerest apologies for the delayed response here, we’ve been dealing with a higher-than-usual volume following our release and we’re working as quickly as we can to get back to everyone.

I wanted to check in on this thread to see if you were still running into issues getting Arc squared away on your home network?

I’ll be monitoring this thread for your reply :pray:

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