A sealing unit for a cabinet containing optical components. A gasket defines a plurality of apertures configured to provide a seal around a plurality of optical fiber cables, wherein the gasket has an interior side intended to face the interior of the cabinet and an exterior side intended to face an exterior of the cabinet. A first retaining device is located on the interior side of the gasket, and a second retaining device is located on the exterior side of the gasket. The first and second retaining devices each include a plurality of channels, wherein each channel is aligned with a respective aperture of the gasket and each channel is configured to receive one of the plurality of optical fiber cables. Each channel has a profile defined by a plurality of protruding surfaces configured to restrain longitudinal movement of an optical fiber cable received therein.