CCIE RS MPLS terminology and forwarding work principle

1) MPLS terminology
Label: Similar to the role of the destination IP address, the router forwards the data based on the label. It is a relatively short, fixed-length, usually only local-specific identifier. These labels are usually located between the data link layer encapsulation header and the Layer 3 data packet of the data link layer. The label is mapped to the FEC through the binding process. .
LIB: A tag information base that obtains tag values ​​through a tag protocol.
LFIB: The label forwarding information base is generated based on the LIB and is used to guide the forwarding of MPLS packets.
FEC: Forwarding Equivalence Class, a group of data packets that are processed in an equivalent manner during the forwarding process. A routing entry is an FEC. The MPLS router generates a label for each FEC (Route Entry). The FEC can be created by using an address, a tunnel, a COS, etc., and only one route in the MPLS currently seen corresponds to one FEC. Usually the same label is assigned to one FEC on one device.
LSP: Label switching channel. The path taken by the data stream is related to MPLS VPN. An FEC data stream is assigned a certain label at different nodes, and data forwarding is performed according to these labels.
LSR: Label Switching Router. The LSR is the core switch of the MPLS network. It provides label switching and label distribution.
LER: Label Switching Edge Router. At the edge of the MPLS network, traffic entering the MPLS network is divided into different FECs by the LER, and corresponding labels are requested for these FECs. It provides traffic classification and label mapping, label removal.
The LDP neighbor does not send the label learned from the neighbor to the neighbor, and the local is valid. The label that is passed to the neighbor is generated by itself.
(2) Working principle of MPLS forwarding

In local label: The Label Distribution Protocol (LDP) assigns a unique label value to each local FEC.
Out remote label: LDP obtains the label assigned by the neighbor to the FEC, and selects the optimal placement into the FIB.

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