OpenVPN - cipher "BF-CBC"

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OpenVPN - cipher "BF-CBC"

71
7
NAS
DS718+
Router
  1. RT2600ac
Operating system
  1. Windows
Mobile operating system
  1. iOS
So, after updating the openvpn client application (2.5.0) on my win 10 laptop, I get the following error message in the openvpn:

2021-01-01 18:17:22 DEPRECATED OPTION: --cipher set to 'AES-256-CBC' but missing in --data-ciphers (AES-256-GCM:AES-128-GCM). Future OpenVPN version will ignore --cipher for cipher negotiations. Add 'AES-256-CBC' to --data-ciphers or change --cipher 'AES-256-CBC' to --data-ciphers-fallback 'AES-256-CBC' to silence this warning.

I'll be honest: I don't understand what this means. The vpn connection still worked. I tried changing "cipher AES-256-CBC" in my current openvpn config file to "data-ciphers-fallback AES-256-CBC" (I believe that is what it says to do above), but that only created another error that made my connection actually fail. Openvpn has a writeup on this change on this page (under 2.5 notes).

So, since my connection is still working, I'm more just curious. Maybe Synology updated the vpn server already to help with the cipher. Maybe this will cause my connection to fail in future updates to openvpn client apps on W10. I don't know. Just prepping. Interested to see what others know about it here.
 
So, I fixed this by adding, the below in to my config file, as suggested here (though it looks like "ncp-ciphers" is now just "data-ciphers". I'll be honest and say I don't really understand why this works, but I no longer get the error and it is the suggested work around by openvpn.
--ncp-ciphers AES-256-GCM:AES-256-CBC:BF-CBC

Seems to me that maybe the openvpn edition that synology has in our DSM is dated.
 

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