Unable to launch 3DxNLServer

[fractalic]

Currently, every time I attempt to launch 3DxNLServer, I get this error in `3dxnlserver.log`:

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m_websocket_server.listen exception 49 Can't assign requested address
Cannot find port to listen on

This sounds like an issue with binding the 8181 port that the Navigation Library Server needs, but I'm unable to find anything on my system restricting this. `lsof -i` shows no processes listening on 8181 tcp or udp; I've also shut down every cloud storage system, VPN, and network filter (including the system firewall), and the error persists.

I'm able to reproduce the exact same error log on my Macbook running Sequoia 15.7.1, as well as on my Mac Mini running Tahoe 26.0.1 (and which also has very few programs installed

Is there a way to continue diagnosing this?

I had to solve a similar issue with the SpaceMouse not working in Onshape 3 years ago (https://forum.3dconnexion.com/viewtopic ... 89#p116189), where I needed to ensure certificates were properly installed in firefox and that the 3DxNLServer process was actually running, but unfortunately this time I'm not even able to launch the process.

[fractalic]

As of today, I see that sometimes the app runs a little longer before crashing (I'm sometimes able to see it briefly in Activity Monitor).

As a test, I tried binding TCP *:8181 in Python, and that worked fine, so I'm not sure what's up with 3DxNLServer. If I could launch it and get more log info, that could be helpful

[fractalic]

Another thing I've tried: restart in safe mode, disable firewall, disable all network content filters, manually grant {full disk access, accessibility, input monitoring} to 3DxNLServer -> still the app crashes, still the same error.

what on earth is the driver doing? why can't it bind to a port that isn't being used by anything else?

[fractalic]

I've finally figured out what on earth the driver is doing! I had entirely given up on ever being able to use my SpaceMouse in OnShape again, until I unexpectedly noticed 3DxNLServer showing up in Activity Monitor on my mac mini, and I realized I could binary search through my config until I worked out what was different between the systems.

3DxNLServer binds 127.51.68.120:8181, which will fail if this IP is not currently associated to any interface on the system. Thankfully (for my sanity), I can replicate this failure:

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❯ python3
Python 3.14.0 (main, Oct  7 2025, 09:34:52) [Clang 17.0.0 (clang-1700.0.13.3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import socket
>>> server=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
>>> server.bind(("127.51.68.120",8181))
Traceback (most recent call last):
  File "<python-input-2>", line 1, in <module>
    server.bind(("127.51.68.120",8181))
    ~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
OSError: [Errno 49] Can't assign requested address

We need to link this IP to a network interface, in particular the loopback interface lo0, which we can do like so:

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sudo /sbin/ifconfig lo0 alias 127.51.68.120 up

and then see the IP properly associated, via ifconfig:

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❯ ifconfig
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
	options=1203<RXCSUM,TXCSUM,TXSTATUS,SW_TIMESTAMP>
	inet 127.0.0.1 netmask 0xff000000
	inet6 ::1 prefixlen 128 
	inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1 
	inet 127.51.68.120 netmask 0xff000000
	nd6 options=201<PERFORMNUD,DAD>
	...

At which point we can bind 127.51.68.120:8181, and so can 3DxNLServer as confirmed by a much more desirable log message in Console:

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<timestamp>: Http and Websocket server successfully started

It's not clear to my why 3DxNLServer is not able to directly check for and optionally create this IP link when it runs, but it turns out there is a configuration installed on the system as part of the SpaceMouse driver install process. This is the file /Library/LaunchDaemons/com.3dconnexion.nlserverIPalias.plist, which contains this:

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>Label</key>
  <string>com.3dconnexion.nlserverIPalias</string>
  <key>RunAtLoad</key>
  <true/>
  <key>ProgramArguments</key>
  <array>
    <string>/sbin/ifconfig</string>
    <string>lo0</string>
    <string>alias</string>
    <string>127.51.68.120</string>
    <string>up</string>
  </array>
</dict>
</plist>

So why wasn't it configured on my system? Because of years of random junk installed on my machine and my obsession with disabling LaunchDaemons that I don't specifically understand and want to run. At some point, I had toggled off this seemingly random entry called "ifconfig" under Login Items and Extensions in my System Settings:

ifconfig.png (24.44 KiB) Viewed 356 times

Toggling it on (or better yet, Loading it via LaunchControl, which is how I initially identified ifconfig as a critical 3dconnexion config), allowed 3DxNLServer to start successfully after a reboot.

I'm so happy to have this fixed, and I think it would be great if the server app could handle this configuration automatically, or at least detect and log it.