Steering data communications packets for transparent, bump-in-the-wire processing among multiple data processing applications in a link-level data communications switch, the switch including data communications ports, a port connected to a first data communications network and another port connected to a second data communications network, other ports connected to the data processing applications, the switch also including rules governing the steering, including receiving in the switch from the first network data communications packets directed to the second network, each packet containing a source network address and a destination network address and steering by the switch each packet among the applications and through an egress port, such steering carried out only in accordance with the rules, using neither the source network address of the packet, the destination network address of the packet, nor any link-level identifier of any application.