network internet connectivity issues with Qubes VM kernel

[adrelanos]

Qubes OS version
R4

Affected component(s) or functionality
Networking.

Brief summary
When using Qubes VM kernel in Debian VMs after a while no new connections are possible. After waiting a few minutes, new connections are possible.

To Reproduce
Steps to reproduce the behavior:
_1. setup Qubes VM kernel in debian-10 TemplateVM
_2. shut down debian-10 based AppVM
_3. do regular internet browsing or other network activity
_4. existing network connections still functional but often no new connections can be opened for minutes

Expected behavior
No connectivity issues.

Actual behavior
Connectivity issues where no causal connection to reproducible steps could be made.

Solutions you've tried
Keeping ping to some destinations running after boot of the VM. Ping will never show any issues and keep going. However, new websites opened in the browser might stop to function. nslookup might also still be available.

No network issues when reverting to Qubes dom0 kernel. (Due to #5212 this is a non-solution long term.)

Related, non-duplicate issues
There was a similar issue maybe 1-2 years ago where a kernel upgrade has lead to sporadic networking issues. Does anyone remember?

//cc @HW42 (iirc was analyzing the previous bug.)

[github-actions]

This issue is being closed because:

• This issue is on the "Release 4.0 updates" milestone.
• Qubes OS 4.0 reached EOL (end-of-life) over one year ago.
• There has not been any activity on this issue in over one year.

If anyone believes that this issue should be reopened and reassigned to an active milestone, please leave a brief comment.
(For example, if a bug still affects Qubes OS 4.1, then the comment "Affects 4.1" will suffice.)