Internal ssh client and server on openSUSE

Client: (the box where you want to connect from)
Do nothing

Server: (the box where you want to connect to)
Start the sshd daemon:
rcsshd start

Use Yast assign the internal zone to the internal LAN interface and make sure port 22 is open (it opens all ports on the internal interface by default unless you tell it to protect from the internal zone)

That's it. Now you can:
ssh user@server

ssh without a password. We create a rsa key and store it on both client and server. We then will not be asked for a password. Here we create the key for root:

1. Login as root and change to /root
ssh-keygen -t rsa

2. ssh to the server:
ssh root@server (e.g. in my case ssh root@hh32.hh3.site)
enter the root password, then:
cd /root
mkdir .ssh
now we are back on the client issue:
cat .ssh/id_rsa.pub | ssh  root@server 'cat >> .ssh/authorized_keys'

Now, root can login to the server without a password