If you are here it’s you are wondering why your are getting a Disconnected: Server protocol violation: unexpected SSH2_MSG_UNIMPLEMENTED packet error on PuTTY.

The reason is you actually use a deprecated SSH key exchange algorithm.

To fix this you can first update your PuTTY version to the latest one. If it’s still doesn’t work, in your PuTTY configuration options go to:

Connection > SSH > Kex

And in the “Algorithm selection policy” move Diffie-Hellman group exchange below the – warn below here – line like the following screenshot.

Save your session configuration and try to connect again.