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LSR
A label switching router (LSR) is a fundamental component on an MPLS network. LSRs support label
distribution and label swapping.
LER
A label edge router (LER) is an LSR that resides at the edge of an MPLS network and is connected to
another network.
LSP
A label switched path (LSP) is the path along which packets of a FEC travel through an MPLS
network.
An LSP is a unidirectional path from the ingress of an MPLS network to the egress. On an LSP, two
neighboring LSRs are called the "upstream LSR" and "downstream LSR," respectively. In
Figure 2 ,
LSR B is the downstream LSR of LSR A, and LSR A is the upstream LSR of LSR B.
Figure 2 Diagram of an LSP
LFIB
Labeled packets are forwarded according to the label forwarding information base (LFIB).
Control plane and forwarding plane
An MPLS node consists of two planes, control plane and forwarding plane.
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The control plane assigns labels, selects routes, creates the LFIB, and establishes and
removes LSPs.
•
The forwarding plane forwards packets according to the LFIB.
MPLS network structure
Figure 3 Diagram of the MPLS network structure