MPLS Unicast IP

MPLS is a protocol that forward packet based on Label instead of IP address. There are several MPLS application, and one of them is MPLS Unicast IP. A router with MPLS Unicast IP is actually forwarding a packet to the same path as a router with IP routing. The difference is only that the MPLS router forwards the packet based on Label. Then why it is important to know what MPLS Unicast IP is? It is important since many of the application is using MPLS unicast IP forwarding as part of the MPLS network.

MPLS has something called Control Plane and Data Plane. The Data Plane are the data structured used by the MPLS in operation.  FIB, LFIB, LIB are the tables that we are talking about. FIB contains information to map IP address and network interface of where a packet destined to an IP address will be forwarded. LFIB contains information to map label and network interface of where a packet with a label will be forwarded. And the LIB is actualy a library of LFIB, which map all labels and ports including the ones which are not currently being used to forward packet. LIB contains only the best map, so that there is only network interface mapped to a label on it. 

Now, how the LIB feeds the LFIB and FIB? 

In simple words, the MPLS routers distribute routing information using EIGRP, OSPF or other routing procotol. From this protocol, the MPLS router will know where is the best route to delivere a packet. The router will pick up the best route, find the related label on the LIB and then update the LFIB.