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MPLS Fundamentals by Luc De Ghein - CCIE No. 1897

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Label Switched Path

A label switched path (LSP) is a sequence of LSRs that switch a labeled packet through an MPLS network or part of an MPLS network. Basically, the LSP is the path through the MPLS network or a part of it that packets take. The first LSR of an LSP is the ingress LSR for that LSP, whereas the last LSR of the LSP is the egress LSR. All the LSRs in between the ingress and egress LSRs are the intermediate LSRs.

In Figure 2-5, the arrow at the top indicates the direction, because an LSP is unidirectional. The flow of labeled packets in the other direction—right to left—between the same edge LSRs would be another LSP.

Figure 2-5. An LSP Through an MPLS Network

The ingress LSR of an LSP is not necessarily ...

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