Tahoe 26 blocking VPN clients accessing remote business networks.

I run a MacBookPro M2 through a Netgear MR7500 Nighthawk M7 wireless broadband modem/router (on the Telstra network).

I use OpenVPN or Tunnelblick VPN client software to connect to a remote business network, and it has been running fine for years.

However after recently upgrading to MacOS Tahoe 26 on my MacbookPro, iPad and iPhone, my M7 is blocking my VPN connections on both OpenVPN and Tunnelblick.

It looks like Apple has removed some legacy IPsec protocols in Tahoe OS which is tripping up the M7. ... and is kind of frustrating as my M7 is only 4 months old.

If I run my iPad, iPhone or Macbook Pro directly through a separate 5G hotspot everything runs as expected.

If I run my iPad, iPhone and MackBook Pro through my MR7500 Nighthawk M7 via a Wi-Fi or wired connection, OpenVPN and Tunnelblick will initally connect, but I cannot access the business network.

Initially I found I needed to run OpenVPN or Tunnelblick through ProtonVPN (tunnel in a tunnel) to access the business network, which effectively hides VPN Traffic from the M7.

I have performed the following without success:

• Reset the M7 back to factory default, but still have the issue.
• Uninstalled and reinstalled VPN software multiple times on all my devices.
• Checked for M7 firmware updates, but appear to have the latest firmware.
• Disabled and re-enabled VPN pass-through on the M7. 

After further testing I have found that setting OpenVPN VPN Protocol = TCP, my MacBookPro and iPhone can connect to my business network without a tunnel-in-tunnel configuration, but my iPad is not able to connect to my business network through the M7 (it can only connect if using another 5G hotspot). I also cannot connect to my business network using Windows 11 on Parallels on my Macbook Pro.

Does anyone have any suggestions on what I can do on my iPad and other devices to fix this situation?