Sink supports are required underneath epoxy resin undermount sinks. These supports are not furnished with the sinks.
Existing undermount sinks will usually have sink supports installed in the sink base cabinet, so when replacing an existing sink just make sure the supports are not discarded.
For new wood and plastic laminate sink base cabinets, strut support channels can be installed on cleats fastened to the interior sides of the cabinet as shown in these details.
Painted steel sink base cabinets typically include supports. Check with the manufacturer when ordering new steel cabinetry.