Did these issues begin if you up to date to Sequoia? I ask as a result of…
Concept #1
macOS 15.0 has been reported (e.g. right here, right here) to trigger points with low stage community visitors like VPN and firewall. So that you is likely to be chasing your tail till Apple releases a repair. You can strive putting in 15.1 which remains to be in beta as I write this, however is secure.
Concept #2
Your DNS decision issues is likely to be brought on by Chrome’s silent hijacking of the system DNS resolver. By default, Chrome will attempt to use its personal resolver/DoH which may trigger the signs you are experiencing.
You’ll be able to disable that characteristic utilizing the instructions under (it isn’t potential through Chrome’s settings UI). Give up Chrome fully after which execute these 2 instructions in a Terminal:
defaults write com.google.Chrome BuiltInDnsClientEnabled -bool false
defaults write com.google.Chrome DnsOverHttpsMode -string off
N.B. After making use of these settings, Chrome will show the deceptive message “Your browser is managed by your group”.
Concept #3
Go to System Settings → Community → click on the (…) ellipsis → Set Service Order. Drag your L2TP VPN to the highest of the record, above your Ethernet/WiFi connections. This adjustments the precedence of the connections, serving to be sure that when related, visitors (particularly DNS) is accurately routed to your company community.
