With the release of macOS Sierra, Apple has updated OpenSSL and SSH. As a result, a number of network devices that were previously administered via SSH from the command line have been impacted. This is due to the fact that, by default, the version of SSH shipping with macOS Sierra doesn’t support older encryption methods. As such, you may see the following error when attempting to establish an SSH session:
Unable to negotiate with 10.0.0.1 port 22: no matching key exchange method found. Their offer: diffie-hellman-group1-sha1
In order to still manage devices what require older encryption, you may create an alias to the ssh command within your BASH shell. To do so, add the following command to your BASH profile (~/.bash_profile):
alias ssh='ssh -oKexAlgorithms=+diffie-hellman-group1-sha1'