Functions of the Control and Data Planes on an LSR
Edge LSR
Routing Protocol
Routing Table
Label Distribution Protocol
Label Information Base
Control Plane
FIB
LFIB
Data Plane
Figure 3-1 shows an edge LSR, which does both routing and label switching.
Four forwarding scenarios could occur in this router:
�¡ An unlabeled IP packet is received and is forwarded unlabeled to a
next hop in the IP network.
�¡ An unlabeled IP packet is received, a label is imposed, and it is
forwarded to a next hop in the MPLS network.
�¡ A labeled packet is received, the label is swapped, and it is forwarded
to a next hop in the MPLS network.
�¡ A labeled packet is received, the label is removed, and it is sent as an
unlabeled, regular IP packet.