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DES-7200 Configuration Guide Chapter 1 MPLS Configuration
1-2
1.1.1 Basic Concepts
MPLS node
The nodes enabled with MPLS can identify the MPLS signaling protocol (control protocol),
support one or more Layer 3 routing protocols (including static routes), and forward packets
based on MPLS labels. Generally speaking, an MPLS node is also capable of forwarding
original Layer 3 packets (such as IP packets).
Forwarding Equivalence Class (FEC)
FEC indicates one type of data packets that are handled in equal cost mode during the
forwarding, such as data packets that have the same prefix in their destination addresses.
The FEC supports different classification methods for different applications. For example, the
FEC classifies IP unicast routes based on the address prefixes. That is, one route
corresponds to one FEC. All the packets in the same FEC are equally handled on the MPLS
network.
Label Switching Router (LSR)
As a core device on an MPLS network, the LSR provides label switching and distribution
functions. As specified by RFC 3031 for MPLS system files, the LSR is also an MPLS node
that is capable of forwarding original Layer 3 packets (such as IP packets or IPv6 packets).
For the MPLS on an IP network, this means that the LSR can also forward normal IP packets.
Label Switching Edge Router (LER)
Located on the edge of an MPLS network, the LER identifies different EFCs for incoming traffic,
requests labels for these FECs, and restores the original packets for outgoing traffic by popping
out the labels. The LER thus provides traffic classification, label mapping, and label removal
functions.
Label Switched Path (LSP)
One FEC data stream is assigned with specific labels on different nodes and transmitted along
the nodes according to the switching of assigned labels. The path that the data stream travels is
an LSP. It is a collection of several LSRs. In this manner, you can consider the LSP as a tunnel
that traverses the MPLS core network.
Next Hop Label Forwarding Entry (NHLFE)
The NHLFE table is used to store the next-hop information about MPLS packets. The NHLFE
entries generally cover the following information:
1. Next hop of data packets
2. Link layer encapsulation of data packets to be forwarded
3. Encoding method in the label stack of data packets to be forwarded