"CONNECTION_REFUSED", doesn't say what port

[antifuchs]

Description

I have a Denon AVR-X3500H that is reachable on the network that the remote lives on (I can view the web-based configurator by visiting its IP address and telnet picks up). However, it's not possible to add that receiver to the remote: The remote fails connecting neither when discovering the receiver's address or entering its IP address: Both times it fails with: "Something went wrong when trying to setup a new integration." / Error: CONNECTION_REFUSED.

It doesn't say what port it tried to connect to that refused the connection, and I haven't so far been able to find out.

How to Reproduce

1. Have a denon AVR with network rechable at 10.0.5.27
2. Have remote reachable at 10.0.5.16, same subnet (/24)
3. home-assistant is connected to the receiver via its Denon integration, too.
4. Add the denon integration and specify 10.0.5.27 as the IP address
5. wait
6. receive "CONNECTION_REFUSED".

Expected behavior

I was hoping the integration could tell me what port it was connecting to or what operation it was performing that hit the connection refused status. But ideally, it should connect to the receiver & work...

Integration version

remote version v1.5.2; integration version isn't shown on un-added integrations.

Additional context

I wonder if this is due to my having hass connected to the receiver; but I can connect a browser to the receiver without any issues... Please let me know how I can diagnose this better!

[splattner]

Denon only allows for one telnet connection. When your HASS is connected, it uses telnet by default (if you haven't changed the setting or if you use the integrations since beginning, then it was http only and for those migrating, they left in on http).
So if you try also to connect via telnet with your remote, it won't work.

[zehnm]

That depends on the model and maybe even on the production year. My AVR-X2700 allows multiple telnet connections. I use HA and the UCR Denon integrations at the same time, but I know of other models which only allow a single connection. Unfortunately I couldn't find any official information which models support multiple connections.
Try and error seems to be the only option at the moment.