After LDP activated a FEC for a specified prefix and programmed RTM, it also programs the ingress Tunnel Table in forwarding engine with the LDP tunnel information.
When an IPv4 packet is received on an ingress network interface, or a subscriber IES interface, or a regular IES interface, the lookup of the packet by the ingress forwarding engine results in the packet being sent labeled with the label stack corresponding to the NHLFE of the LDP LSP when the preferred RTM entry corresponds to an LDP shortcut.
If the preferred RTM entry corresponds to an IP next-hop, the IPv4 packet is forwarded unlabeled.