SSH can set in its identification a version 1.99 (SSH-1.99-xxx).
That means the client/server is compatible with SSHv1 and SSHv2.
So the version choice depends of the both side.
1.99 : 1.99 => 2.0
1.99 : 1.x => 1.x
1.99 : 2.0 => 2.O
(see "Compatibility With Old SSH Versions" in RFC 4253)
