OpenSSH 6.5 and 6.6 sometimes encode a value used in the
    curve25519 key exchange incorrectly, causing connection failures
    about 0.2% of the time when this method is used against a peer that
    implements the method properly.
    
    Fix the problem and disable the curve25519 KEX when speaking to
    OpenSSH 6.5 or 6.6. This version will identify itself as 6.6.1
    to enable the compatability code.
    
    openssh-6.6.1p1