ssh  root@IP -p 22 -v

Unable to negotiate with IP port 22: no matching key exchange method found. Their offer: diffie-hellman-group1-sha1

ssh -oKexAlgorithms=+diffie-hellman-group1-sha1 root@IP -p 22 -v
Тук вече се конектва правилно!

Има и друг вариант

Файл:  /etc/ssh/ssh_config:

Host *
GSSAPIAuthentication yes
KexAlgorithms +diffie-hellman-group1-sha1