@AurelioS 

Try and add cipher AES-256-gcm in the ovpn config file. default is cipher AES-128-CBC
 

  @MR.S 

Oh, this worked. It should be a config option in the UI.

I tried it with data-ciphers AES-256-GCM in the config file, but that fails.

And this is strange. That's the option you should use according to the docs when using an OpenVPN client 2.6.x

  @AurelioS 

I didn't quite understand what you meant, did setting AES-256-GCM in the configuration file work or not?

  @MR.S 

Yes, it works with the line "cipher AES-256-GCM" however I'm not really sure there is no silent fallback to AES-128-CBC

If you use the line "data-ciphers AES-256-GCM" instead you will receive an error message:

OPTIONS ERROR: failed to negotiate cipher with server.  Add the server's cipher ('AES-128-CBC') to --data-ciphers (currently 'AES-256-GCM') if you want to connect to this server

This is also strange because the change log of firmware version 1.2.2. mentions this and I have 1.3.3: 

- Upgrade the OpenSSL version.

- Support GCM encryption of OpenVPN.

ER8411(UN)_V1_1.2.2 Build 20240809 | Omada Network Support

Ok, this seems to work:

data-ciphers AES-256-GCM:AES-128-GCM:AES-128-CBC

With verbose logs on you can see the line in the log file:

Outgoing Data Channel: Cipher 'AES-256-GCM' initialized with 256 bit key
Incoming Data Channel: Cipher 'AES-256-GCM' initialized with 256 bit key
Data Channel: cipher 'AES-256-GCM', compression: 'stub'

  @AurelioS