After updating my open ssh client today I found myself unable to connect to our legacy server:
$ ssh legacy.example.com Unable to negotiate with legacy.example.com port 12345: no matching key exchange method found. Their offer: diffie-hellman-group1-sha1
And learned something new about ssh. This can be solved on the client side by allowing the legacy algorithm for this server:
Host legacy.example.com KexAlgorithms +diffie-hellman-group1-sha1
Hopefully the server side get's an update soon...