|  | 6.4 | Frame Relay Subinterfaces
| 6.4.2 | Split horizon routing environments
Split horizon reduces routing loops by not allowing a routing update received on one physical interface to be sent back out that same interface. As a result, if a remote router sends an update to the headquarters router that is connecting multiple PVCs over a single physical interface, the headquarters router cannot advertise that route through the same physical interface to other remote routers.