With OS X 10.12 the version of OpenSSH is v7 and some encryption algorithms have been removed. For our old Cisco catalyst is diffie-hellman-group1-sha1
When I use iTerm is OK with this cmd :
ssh -p22 -o KexAlgorithms=+diffie-hellman-group1-sha1 firstname.lastname@example.org
But where can I put this option in RoyalTSX, I have tried custom cmd but don't work
go to the "Advanced - SSH" settings of your SSH connection and enter "-o KexAlgorithms=+diffie-hellman-group1-sha1" (without quotes) in the "Additional SSH Options" field.