Please help me diagnose knotty routing problem

[el_pedr0]

Summary: I see different behaviour when I use the ip address of an internal machine compared to when I use it's hostname concatenated with the RT-AC68U's Domain Name. Please help me diagnose what's going on.

Symptoms:
I have an audiobookshelf instance on a host called abshost in my home network which allows me to stream audiobooks. I also have the audiobookshelf android app. I can configure the app to point to my server either using the address: 192.168.xxx.xxx:13378, or using the abshost.home.real.domain:13378 where home.real.domain is the value set in the RT-AC68U's Domain Name field of LAN > LANIP. (for this thread I've replaced a real domain that I own with 'real.domain').
Within the app, there is a 'cast' button which I can click to cast the stream to my chrome cast devices.
When I click the cast button, I can hear the chime on the speakers indicating that a connection is being established. However, the stream only makes it to the speakers when I have configured the app using the IP address rather than the abshost.home.example.com. The app itself can accept urls rather than ip addresses.

In both cases, the traffic has to be handled by the router to route it to the host. But why should it behave differently when it adds an internal DNS lookup to resovle the abshost.home.real.domain? The subdomain home.real.domain is defined within the router configuration as the router's Domain Name, and while the root real.domain has public records, the home.real.domain does not appear in any public dns records.

How can I start diagnosing what's going on here?

(edited to clarify addresses)

 

[Justinh]

Does using only the server's hostname work?

It feels like a loopback problem. I've hit this with my local Emby server where I could get the server was auto-detected but I couldn't actually use it from a guest wireless connection.

Does your server have any logging that gives a hint?

 

[el_pedr0]

Oh! You've unearthed yet more behaviour. When I configure the app to point to abshost:13378, it successfully connects to the server. But the Cast button has disappeared completely!
Correction: I realised that the chromecast button had disappeared for all server configurations within the app. So I rebooted the server and the chromecast button is back in all configurations.

So:
192.168.xxx.xxx:13378 -> succesfully streams to chromecast
abshost.home.real.domain:13378 -> Cast button is functional, I can hear the chime as I connect to the device, but audio doesn't stream
abhost:13378 -> Cast button is functional, I can hear the chime as I connect to the device, but audio doesn't stream

I'll dig around for some server logs - unfortunately, I suspect there will be no way to get logs on the app side of things.

Thanks for replying! I recognise that this is a bit of a fringe case, so am grateful that you pitched in!

 

[Justinh]

Might try telling the router what host name to use in LAN management:

 

[eibgrad]

Dealing w/ hostnames and local name resolution when it comes to DNSMasq can be very tricky. Things don't always work as expected.

What I recommend is you following the advice I can to someone else regarding the proper configuration of DHCP, static leases, and DNS.

Cannot bind IP - "This entry already exists."

I am using an ASUS GT-AX6000 with the latest Merlin firmware running. I have 131 manually assigned IPs, and many other static IPs on my network. I have three devices that are getting DHCP assignments from the DHCP server that I cannot customize. When I add the IPs to the list of manually...

www.snbforums.com

IOW, always use DHCP to make your assignments, and create static leases via DHCP for anything that needs or benefits from a fixed IP. Finally, always create host-record directive for each and every device you plan to access by its hostname, both unqualified and fully-qualified.