I Can VNC to a server when it is connected via Lan, but not via WiFi

sancho.s ReinstateMonicaCellio

1/10/24, 11:34 PM

EDIT: I found PC3 had Settings -> Sharing -> Screen Sharing -> Networks -> <Current SSID> enabled, and PC1 had it disabled. Enabling it in PC1 was perhaps needed and I did it, but that didn't solve the problem.

I am VNCing,
Server PC1: Ubuntu ~~20.04.3LTS~~ sudo apt upgraded to 20.04.5LTS, with vino-server.
Client PC2: Win 10 PC2, with tigervnc.

I can VNC PC2 -> PC1 when PC1 is connected to the router via LAN.
I cannot VNC PC2 -> PC1 when PC1 is connected to the router via WiFi (the error message is "unable to connect to socket: Connection timed out (10060)") even when LAN is disconnected and PC1 rebooted (see this). I can surf the web from PC1 (after work described below).

I have another PC3 with Ubuntu 20.04.5LTS, connected only via WiFi.
I can VNC PC2 -> PC3. I don't know what potential differences between PC1 and PC3 to check.

How can I diagnose and solve this?

Notes:

I was able to VNC to PC1 via WiFi until recently. Things that possibly changed:

1.1. My ISP seems to have updated the router firmware, as its home page changed slightly. I cannot tell if anything else changed. I pressed the reset button of the router, and reinstated my WiFi SSID/password.

1.2. I was not able to connect from PC1 to the internet (I don't know if prior to resetting the router I could). Adding nameserver 8.8.8.8 to /etc/resolv.conf (it only had nameserver 127.0.0.53) solved the issue. I then set /etc/resolv.conf as a symlink to a custom file, instead of the default, to avoid it being rewritten. I wouldn't know why all these changes (or perhaps only one of them) required customization of /etc/resolv.conf. After upgrading to 20.04.5LTS this is still needed.
In PC3 /etc/resolv.conf only has nameserver 127.0.0.53, and I can both connect from PC3 to the internet, and VNC from PC2 to PC3. Also puzzling.

Related:

Ubuntu Server 17.04 reachable via LAN, but not via WAN interface (but not about VNC).

111

0 + 4

vnc

networking

dns

20.04

guiverc

1/11/24, 12:20 AM

Are you details correct? ie. you're asking about a machine that is a year behind (*or more*) on security fixes & patches? ([20.04.5 ISO release date is shown here](https://fridge.ubuntu.com/2022/02/25/ubuntu-20-04-4-lts-released/) but installed systems upgraded in the weeks before that, and all systems have reported as [20.04.5](https://fridge.ubuntu.com/2022/09/01/ubuntu-20-04-5-lts-released/) for some time now.

guiverc

1/11/24, 2:00 AM

Your PC3 shows you've applied security fixes & upgrades as per my prior comment, where as the PC1 is a year or more behind on security fixes; if PC1 is using HWE it's using an *unsupported* kernel etc. (*maybe read-read my first comment & check your provided details, and what security changes you've made that possibly blocked fixes occurring etc... 20.04.3 alone shows a potentially significant issue (esp. regards security) unless you made a mistake in your question*)

guiverc

1/11/24, 2:15 AM

FYI: If you install a Ubuntu system, eg. 20.04 using any media (20.04, 20.04.1, 20.04.2, 20.04.3, 20.04.4, 20.04.5 etc) on applying all upgrades to the system it'll upgrade to the latest available & report as such. The installation media used dictates kernel stack & other system defaults, so if a GA kernel stack media is used for install; the kernel will remain 5.4 for 20.04.1 thru 20.04.5, where as with HWE it'll change from 5.4, 5.8 (20.04.2), 5.11 (20.04.3), 5.13 (20.04.4) before final HWE kernel of 5.15 at 20.04.5, with all reporting as latest available (kernel stack choice isn't release)

sancho.s ReinstateMonicaCellio

1/11/24, 1:35 PM

@guiverc - I didn't know what you clarified. Nevertheless, I upgraded PC1 to 20.04.5LTS, and I still see the same issues: 1) I need a custom `/etc/resolv.conf` to surf the web. 2) I cannot VNC on WiFi. 3) Anything else? So that was not the (only) source of the problem. I must have HWE kernel, since it is now 5.15.0.57.

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