Programmable switches and routers are described herein for enabling their internal network fabric to be configured with a topology. In one implementation, a programmable switch is arranged in a network having a plurality of switches and an internal fabric. The programmable switch includes a plurality of programmable interfaces and a buffer memory component. Also, the programmable switch includes a processing component configured to establish each of the plurality of programmable interfaces to operate as one of a user-facing interface and a fabric-facing interface. Based on one or more programmable interfaces being established as one or more fabric-facing interfaces, the buffer memory component is configured to store packets received from a user-facing interface of an interconnected switch of the plurality of switches via one or more hops into the internal fabric.