The only way I can find to configure ssh on a router vty is as follows
crypto rsa generate rsa line vty 0 15 transport input ssh
The problem is that the crypto line cannot be entered without having
ip domain name
which is not part of our standard config. (Before anyone asks, we use ip domain lookup to specify the domains to search on the box itself; and we prefer to not have a domain name in order to stop it appearing in CDP, and management systems. All our router names are unique so we don't need the domain name.)
It seems we can configure a domain name, generate the rsa key, then remove the domain name; or we can set a short domain name - such as a dot(.). Either one works .... but is there a way to avoid this? Any guidance appreciated. FWIW the following link applies