  We demonstrate a technique for locking the frequency of a tunable diode laser
to a ring-cavity resonator. The resonator is stabilized to a diode laser which
is in turn locked to an atomic transition, thus giving it absolute frequency
calibration. The ring-cavity design has the principal advantage that there is
no feedback destabilization of the laser. The cavity has a free-spectral range
of 1.3 GHz and $Q$ of about 35, which gives robust locking of the laser. The
locked laser is able to track large scans of the cavity.
