I found this post because it was the first result in a DuckDuckGo search for "armbian kex_exchange_identification"
If your armbian device is at IP address 192.168.1.5, then the short answer is to simply do the following for first login:
ssh -o HostkeyAlgorithms=+ssh-rsa root@192.168.1.5
The answer is sorta described on this answer elsewhere in the forums. Back in 2022, OpenSSH decided to retire (to deprecate) the SHA-1 hash combined with the RSA public key algorithm (read more here). This means that in most major operating systems (Windows, Linux, Mac) that use OpenSSH as their ssh client, the rsa-sha key exchange is deactivated by default. I'm not sure why, but it appears that the sshd on Armbian doesn't offer any other KexAlgorithms, even though it could. So your Armbian device doesn't offer a KexAlgorithm that your laptop/desktop/other device likes.
I installed v24.11 rolling for Orange Pi PC running Armbian Linux 6.6.44-current-sunxi yesterday (29 Sept 2024) and sshd was still configured this way.
If you want a permanent fix, you can add 2 lines to your /etc/ssh/sshd_config file on your Armbian device:
KexAlgorithms ecdh-sha2-nistp256
HostKeyAlgorithms rsa-sha2-256
Then run sudo service sshd restart and it will restart using the new key exchange algorithms and you'll be able to connect without special effort.
