ESXi 6.0 update 2 uses OpenSSH 7.1 has one of our encryption algorithms disabled by default. To remedy this error the encryption algorithm, "diffie-hellman-group1-sha1", must be enabled.
This can be done via the following steps
Login to ESXi console
Go to ssh config directory
Backup existing config
cp sshd_config sshd_config.bak
Add the following line into file and save
Restart SSH service
Now that the "diffie-hellman-group1-sha1" algorithm has been enabled, you should no longer encounter errors when connecting to your ESXi host.
Last Update: 23 June, 2017