Link-level data communications carried out in a link-level data communications switching apparatus that includes modular link-level data communications switches; the switching apparatus is configured as two layers of link-level data communications switches; all the switches stacked by a stacking protocol that shares administrative configuration information among the switches and presents the switches as a single logical switch; the switching apparatus includes data communications ports coupling the switching apparatus to data communications networks and to service applications, each service application associated with a unique, link-level identifier; the switching apparatus includes rules governing the steering of packets among service applications and networks; including receiving, in the switching apparatus, packets directed to a destination network; and steering each packet among the service applications to the destination network in accordance with the rules, without using the link-level identifier of any service application.