Disconnections from VPN and Chrome refusing to load pages

Question

I have a VPN I use for work with L2TP config. The same VPN works smoothly without any issue in a Windows laptop. However, it drives me crazy in my iMac with two issues.

1. We have a few websites from work that are only accessible through VPN. Chrome refuses to open those sites and I get instantly an error of 'ERR_NAME_NOT_RESOLVED'. I get this more than 24 hours now. I tried to flush DNS and reset my router, but still. The same websites are accessible with Safari, but it is super slow and not reliable. Direct access on ftp or database works without an issue.

2. There are days that I get disruptions on VPN. Specifically, I have it with disabled the option of getting all traffic through the VPN. But, in those days, when I try to open any website (no work related), it keeps loading and loading until I get disconnected from the VPN and then suddenly the page loads. I might get a disconnection every 2-3 minutes.

I want to focus that at the same time, Windows laptop works great with it, and our IT department cannot see anything strange in their side.

I have an iMac with Sequoia 15.0

Edit: More things I tried to do

• Disable firewall
• Reset Chrome settings
• Remove all addons
• Delete VPN configuration and create it again
• Flush Chrome DNS through the internal settings

Answer 1

Did these problems start when you updated to Sequoia? I ask because...

Idea #1

macOS 15.0 has been reported (e.g. here, here) to cause issues with low level network traffic like VPN and firewall. So you might be chasing your tail until Apple releases a fix. You could try installing 15.1 which is still in beta as I write this, but is stable.

Idea #2

Your DNS resolution problems might be caused by Chrome's silent hijacking of the system DNS resolver. By default, Chrome will try to use its own resolver/DoH which could cause the symptoms you're experiencing.

You can disable that feature using the commands below (it's not possible via Chrome's settings UI). Quit Chrome completely and then execute these 2 commands in a Terminal:

defaults write com.google.Chrome BuiltInDnsClientEnabled -bool false
defaults write com.google.Chrome DnsOverHttpsMode -string off

N.B. After applying those settings, Chrome will display the misleading message "Your browser is managed by your organization".

Idea #3

Go to System Settings → Network → click the (...) ellipsis → Set Service Order. Drag your L2TP VPN to the top of the list, above your Ethernet/WiFi connections. This changes the priority of the connections, helping ensure that when connected, traffic (especially DNS) is correctly routed to your corporate network.

Update 2024-10-01

Mullvad (one of the largest public VPN providers) is tracking a related issue #6521 on their GitHub. The following comment was recently posted to it:

According to Feedback Assistant it seems that Apple is aware of the issue and is working on a fix.

"Apple services break when using VPN due to service updating issue — FB15325958 / Potential fix identified"