No ARC connection on Telenet modem (ref#3FKRFL)

Support
1

Network Setup

· My only router was provided by my ISP

ARC Status

· ARC is *Not Ready*

Roon Error Code

· “natpmp_autoconfig”: {“status”:“NotFound”}, “upnp_autoconfig”: {“status”:“NotFound”} }

Have you successfully located and enabled the UPnP or NAT-PMP settings in your router's web UI?

· I've turned UPnP/ NAT-PMP on and ARC won't connect

Select the Diagnostic Keyword or Text String

· Something else

Don't give up yet.

· I'm stuck. I'd like to create a post to ask Roon Community for help.

Describe the issue

no ARC connection on Telenet modem

Describe your network setup

ISP: Telenet - modem F@ST3896LG-TN - Roon running on NAS Synology DS918+

Tried to use UPnP: did not work
port forwarding rule added: TCP connection, internal and external port 55002 : not working

2

Hello @infotom ,

Roon ARC issues on Telenet hardware with a Synology NAS are a known problems. The NotFound error usually means that Roon cannot “talk” to your router, even if you’ve set up the rules.

Here is a step-by-step checklist to troubleshoot this:

1. Check for CGNAT (Carrier-Grade NAT)

Telenet often uses CGNAT, which means your ISP shares one public IP across many customers. If this is the case, port forwarding on your router won't do anything because the traffic is blocked upstream at the ISP level.
  • How to check: Log into your Telenet modem settings and find your WAN IP. Then, visit  http://whatsmyip.org .
  • If the numbers don't match: You are behind a "private" IP. Call Telenet support and ask to be switched to a "Public IPv4 address" (they usually do this for free upon request).

2. Check Synology DSM Firewall

Since your Roon Core is on a NAS, the NAS firewall might be blocking the connection.
  • Go to Control Panel -> Security -> Firewall.
  • Ensure that port 55002 (TCP) is allowed for incoming connections.
  • If using Docker: Make sure the Roon container is set to "host" network mode. If it’s set to "bridge," the port forwarding will go nowhere.

3. Manual Port Forwarding (Telenet F@ST3896LG-TN)

UPnP on these modems is notoriously unreliable. It is better to do this manually:
  1. Static IP: Ensure your Synology NAS has a static internal IP reserved in your router's DHCP settings.
  2. Disable UPnP: Turn it off in the modem settings to avoid conflicts with your manual rules.
  3. Port Forwarding: Delete old rules and create a new one:
    • Protocol: TCP
    • Internal/External Port: 55002
    • Target IP: The static IP of your Synology NAS.

4. The "Easy Way" (Tailscale)

If Telenet won't give you a public IP, or if the port forwarding still isn't working, stop fighting the router. Install Tailscale on both your Synology and your mobile device. It creates a secure, encrypted tunnel between your phone and your NAS that completely bypasses the need for port forwarding. It’s a game-changer for Roon ARC.
3

Hi @infotom,

This provider (Telecom) is broadly rumored to implement CG-NAT. This will break port forwarding above the level of your account. Unfortunately, there’s no solution within Roon for this. You’ll need to either:

a) reach out to your ISP directly and ask for a dedicated external IPv4 address

or

b) setup Tailscale (a VPN) as an alternative to port forwarding:

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Hi @infotom,

We’re going to tentatively mark the response above as a Solution since it works for the vast majority of users with the symptom you reported.

This thread will remain open for a few days, however. Please reach out if you require any help setting up Tailscale.

Thank you!

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